How to solve the heat dissipation problem of PCB circuit board? Master these 10 correct methods.

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Controlling heat or heat dissipation and distribution is very important in building and using PCB circuit boards, and failing to manage heat transfer can also ruin your board. For electronic equipment, a certain amount of heat will be generated during operation, causing the internal temperature of the equipment to rise rapidly. If the heat is not dissipated in time, the equipment will continue to heat up, and the device will fail due to overheating. The reliability of electronic equipment Performance will decrease. Therefore, it is very important to handle the heat dissipation of the circuit board well.

1. Heat dissipation through the PCB board itself. The currently widely used PCB boards are copper-clad/epoxy glass cloth base materials or phenolic resin glass cloth base materials, and there are also a small amount of paper-based copper-clad sheets. Although these substrates have excellent electrical properties and processing properties, they have poor heat dissipation. As a heat dissipation path for high-heating components, it is almost impossible to expect the PCB resin itself to conduct heat, but to dissipate heat from the surface of the component to the surrounding air. However, as electronic products have entered the era of component miniaturization, high-density installation, and high-heat assembly, it is not enough to rely solely on the surface of components with very small surface areas to dissipate heat. At the same time, due to the extensive use of surface-mounted components such as QFP and BGA, the heat generated by the components is transferred to the PCB board in large quantities. Therefore, the best way to solve the problem of heat dissipation is to improve the heat dissipation capacity of the PCB itself that is in direct contact with the heating component, through the PCB board Conduct or radiate out.

2. Add radiators and heat conduction plates to high-heating devices. When there are a few devices in the PCB that generate a large amount of heat (less than 3), you can add a radiator or heat pipe to the heating device. When the temperature still cannot drop, A radiator with a fan can be used to enhance the cooling effect. When there are a large number of heating devices (more than 3), a large heat dissipation cover (board) can be used. It is a special radiator customized according to the position and height of the heating device on the PCB board or placed on a large flat-panel radiator. Cut out the high and low positions of different components. Attach the entire heat dissipation cover to the component surface and make contact with each component to dissipate heat. However, due to the poor consistency of the components during assembly and soldering, the heat dissipation effect is not good. Usually, a soft thermal phase change thermal pad is added to the component surface to improve the heat dissipation effect.

3. For equipment that uses free convection air cooling, it is best to arrange the integrated circuits (or other devices) vertically or horizontally.

4. Use reasonable wiring design to achieve heat dissipation. Since the resin in the board has poor thermal conductivity, and copper foil lines and holes are good conductors of heat, increasing the remaining rate of copper foil and adding thermal holes are the main means of heat dissipation. To evaluate the heat dissipation capability of PCB, it is necessary to calculate the equivalent thermal conductivity (nine eq) of the insulating substrate for PCB, which is a composite material composed of various materials with different thermal conductivity.

5. Devices on the same printed board should be arranged according to their heat generation and heat dissipation degree as much as possible. Devices with small heat generation or poor heat resistance (such as small signal transistors, small-scale integrated circuits, electrolytic capacitors, etc.) should be placed In the uppermost part of the cooling airflow (at the entrance), devices with high calorific value or good heat resistance (such as power transistors, large-scale integrated circuits, etc.) are placed at the most downstream part of the cooling airflow.

6. In the horizontal direction, high-power devices should be arranged as close to the edge of the printed board as possible to shorten the heat transfer path; in the vertical direction, high-power devices should be arranged as close to the top of the printed board as possible to reduce the temperature impact of these devices on other devices when they are working. Impact.

7. The heat dissipation of the printed boards in the equipment mainly relies on air flow, so the air flow path must be studied during design and the devices or printed circuit boards should be reasonably configured. When air flows, it always tends to flow in places with low resistance, so when configuring devices on a printed circuit board, avoid leaving a large air space in a certain area. The same issue should also be paid attention to in the configuration of multiple printed circuit boards in the whole machine.

8. Devices that are sensitive to temperature are best placed in the area with the lowest temperature (such as the bottom of the device). Never place it directly above the heating device. It is best to arrange multiple devices staggered on the horizontal plane.

9. Arrange the devices with the highest power consumption and heat generation near the best heat dissipation location. Do not place high-heat components in the corners and edges of the printed board unless a heat sink is arranged nearby. When designing the power resistor, choose a larger device as much as possible, and make sure there is enough space for heat dissipation when adjusting the printed board layout.

10. Avoid the concentration of hot spots on the PCB, distribute the power evenly on the PCB as much as possible, and keep the PCB surface temperature performance uniform and consistent. It is often difficult to achieve strict uniform distribution during the design process, but areas with too high power density must be avoided to avoid hot spots that may affect the normal operation of the entire circuit. If possible, it is necessary to conduct thermal efficiency analysis of printed circuits. For example, the thermal efficiency index analysis software module added to some professional PCB design software can help designers optimize circuit design. The above are some techniques and methods for heat dissipation, which require engineers to continuously accumulate in practice.

Principles for selecting electronic components, how to choose PCB components?

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Components are the basic elements that constitute a circuit and are the final result of circuit principle analysis and calculation. In circuit principle analysis, it is necessary to know the structure, characteristics, parameters of each component, its role in the circuit, and its impact on the entire circuit; in circuit parameter calculation, each component parameter is also a factor in circuit calculation. The final result facilitates the reasonable selection of component specifications and models. Correct selection of components is the key to realizing circuit functions, and selection methods and techniques are very important. How to quickly select components in PCB design?

1. Consider the choice of component packaging

Throughout the schematic drawing stage, component packaging and land pattern decisions that need to be made during the layout stage should be considered. Here are some suggestions to consider when selecting components based on their package.

Remember, the package includes the component’s electrical pad connections and mechanical dimensions (X, Y, and Z), which is the shape of the component body and the pins that connect to the PCB. When selecting components, consider any mounting or packaging constraints that may exist on the top and bottom layers of the final PCB. Some components (such as polarized capacitors) may have height headroom restrictions that need to be considered during the component selection process. When you first start designing, you can start by drawing a basic circuit board outline shape, and then place some large or location-critical components (such as connectors) that you plan to use. In this way, a virtual perspective view of the circuit board (without wiring) can be seen intuitively and quickly, and the relative positioning and component height of the circuit board and components are given relatively accurately. This will help ensure that the components fit properly into the outer packaging (plastic, case, frame, etc.) after the PCB is assembled. Call the 3D preview mode from the tools menu to browse the entire board.

The land pattern shows the actual pad or via shape of the soldered device on the PCB. These copper patterns on the PCB also contain some basic shape information. The size of the land pattern needs to be correct to ensure proper soldering and to ensure the correct mechanical and thermal integrity of the connected components. When designing the PCB layout, you need to consider how the board will be manufactured or, if soldered by hand, how the pads will be soldered. Reflow soldering (where flux is melted in a controlled, high-temperature furnace) can handle a wide variety of surface-mount devices (SMDs). Wave soldering is generally used to solder the reverse side of the circuit board to secure through-hole components, but it can also handle some surface-mount components placed on the back of the PCB. Typically when using this technique, the underlying surface mount components must be aligned in a specific orientation, and the pads may need to be modified to accommodate this soldering method.

Component selection can be changed throughout the design process. Determining early in the design process which devices should use plated through holes (PTH) and which should use surface mount technology (SMT) will help with overall PCB planning. Factors to consider include device cost, availability, device area density, power consumption, etc. From a manufacturing perspective, surface-mount devices are generally cheaper than through-hole devices and generally have higher availability. For small and medium-sized prototype projects, it is best to use larger surface-mount devices or through-hole devices, which not only facilitates manual soldering, but also facilitates better connection of pads and signals during error checking and debugging.

If there is no ready-made package in the database, a custom package is usually created in the tool.

2. Use good grounding methods

Make sure the design has adequate bypass capacitors and ground planes. When working with integrated circuits, make sure to use appropriate decoupling capacitors close to the power supply terminals to ground (preferably the ground plane). The appropriate sizing of the capacitor depends on the specific application, capacitor technology, and operating frequency. When bypass capacitors are placed between the power and ground pins and placed close to the correct IC pins, the electromagnetic compatibility and susceptibility of the circuit can be optimized.

3. Assign virtual component packages

Print a bill of materials (BOM) for inspection of virtual components. Virtual components do not have associated packages and will not be passed to the layout stage. Create a bill of materials and view all virtual components in your design. The only entries should be for power and ground signals, as they are considered virtual components and are only handled exclusively in the schematic environment and are not transferred to the layout. Unless used for simulation purposes, components shown in the virtual section should be replaced with components with encapsulation.

4. Make sure you have complete bill of materials data

Check that the bill of materials report contains sufficiently complete data. After the bill of materials report is created, it should be carefully checked to complete any incomplete device, supplier or manufacturer information in all component entries.

5. Sort according to component number

To aid in sorting and viewing the bill of materials, make sure component designations are numbered consecutively.

6. Check for redundant gate circuits

Generally speaking, all redundant gate inputs should have signal connections to avoid floating inputs. Make sure you check any redundant or missing gates and that any unwired inputs are fully connected. In some cases, if the input is left floating, the entire system may not work correctly. Take the dual op amps often used in design. If only one op amp is used in a dual op amp IC component, it is recommended to either use the other op amp, or ground the input end of the unused op amp, and place a suitable unity gain (or other gain ) feedback network to ensure that the entire component can work properly.

In some cases, ICs with floating pins may not function properly within specifications. Typically an IC can operate to meet specifications only if the IC device or other gates in the same device are not operating in saturation and the inputs or outputs are close to or at the component supply rails. Simulation often cannot capture this situation because simulation models generally do not connect multiple parts of the IC together to model the floating connection effect.

Seven factors that affect SMT welding quality.

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SMT (Surface Mount Technology) welding is a commonly used welding method in modern electronic manufacturing. However, SMT welding quality is affected by many factors, and these factors often have an important impact on welding quality. Next, we will introduce in detail the seven factors that will affect the quality of SMT welding.

1. Temperature control

In the SMT welding process, temperature control is very important. Too high or too low temperature will cause the welding quality to deteriorate. Generally speaking, the soldering temperature should be adjusted according to the requirements of electronic components and soldering materials. If the temperature is too high, it may cause damage to electronic components or overheat the solder joints, thus affecting the soldering quality. And if the temperature is too low, the welding point may not reach a sufficient melting temperature, causing the welding to be weak.

2. Beating quality

Blurring is an important link in the SMT welding process, which directly affects the welding quality. When applying paste, it is necessary to ensure that the position and size of the solder joints are consistent with the design requirements, as well as the wettability between the paste and the solder joints. If the paste is uneven or excessive, it may result in too many or too few welding points, thus affecting the welding quality.

3. Solder alloy

Selecting the appropriate solder alloy is also one of the key factors affecting SMT welding quality. A common solder alloy is an alloy of tin and lead. However, due to environmental protection requirements, many places have begun to use lead-free solder alloys. The selection of solder alloy should be determined according to the requirements of electronic components and printed circuit boards to ensure soldering quality.

4. Equipment performance

The performance of the equipment used in SMT welding will also directly affect the welding quality. The stability and accuracy of the equipment are crucial to the control of the welding process. The equipment should be able to provide appropriate functions such as temperature control, paste control and welding parameter control to ensure the stability and consistency of welding quality.

5. PCB design

PCB (Printed Circuit Board) design will also have an important impact on SMT welding quality. Reasonable PCB design should consider factors such as the layout of components, the size and shape of the pads, and the distance between the soldering points and components. Improper PCB design may result in component position deviation, pad size mismatch, or improper spacing between soldering points, thereby affecting soldering quality.

6. Maintenance

The maintenance of SMT welding equipment is also one of the key factors to ensure welding quality. Regular inspection and maintenance of equipment to maintain the stability and accuracy of the equipment is very important for the control of welding quality. In addition, timely replacement of worn parts and keeping equipment clean can also effectively improve welding quality.

7. Operator skills

The skill level of the operator will also directly affect the quality of SMT welding. Skilled operating skills can ensure accurate setting of welding parameters and stable control of the welding process. At the same time, operators should have the ability to solve common problems, such as poor welding, solder joint defects, etc., to improve welding quality.

To sum up, SMT welding quality is affected by many factors. Temperature control, paste quality, solder alloy selection, equipment performance, PCB design, equipment maintenance and operator skills are all important factors that affect SMT welding quality. Only by comprehensively considering and reasonably controlling these factors can we ensure that the welding quality during the SMT welding process meets the requirements.

What are the key points of PCB design?

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PCB design is a vital part of electronic product development. Here are some PCB design points and key considerations:

1. Layout planning: PCB layout planning is the basis of design. The location of components, wiring routes, power supplies, and ground planes must be considered to ensure signal integrity and optimal performance. Minimize the length of the signal line and reduce the delay of signal transmission.

2. Match impedance: Ensure that the impedance of the signal line matches the signal to be transmitted to reduce reflections and signal integrity issues. Interference can be reduced using differential signaling.

3. Power and ground planes: There should be stable power and ground planes on the PCB to reduce electromagnetic interference (EMI) and provide stability in power distribution. This helps reduce the length of the signal return path.

4. Appropriate layers: Multi-layer PCB can be used to isolate different signals and reduce interference between signal layers. Choose the appropriate layer to meet the needs of your circuit.

5. Thermal management: Consider the heat dissipation needs of components to ensure that heat can be effectively dissipated to avoid component damage caused by overheating.

6. Positioning holes and fixing holes: Add positioning holes and fixing holes to the PCB to install and fix the PCB into a housing or other structure.

7. Symbols and Labels: Add clear symbols and labels to components and connections to facilitate maintenance and troubleshooting.

8. Safety and regulations: Ensure that the PCB design complies with applicable safety standards and regulations, especially for electrical safety and electromagnetic compatibility.

9. EMI suppression: Take necessary measures to reduce electromagnetic interference, such as adding shields, ground planes, filters, etc.

10. Material selection: Select appropriate PCB materials, considering dielectric constant, loss factor and temperature characteristics to meet design needs.

11. Testing and verification: Before actual manufacturing, use simulation tools to verify the performance of the design and conduct prototype testing to ensure that the PCB works properly.

12. Maintainability: Consider the maintainability of PCB to make repair and maintenance work easier.

13. Cost control: Try to reduce PCB manufacturing costs, but do not sacrifice performance and quality.

The importance of PCB design points is to ensure that the circuit board can work properly and have good signal integrity, stability and performance. Therefore, these points need to be carefully considered during the PCB design process.

What is the difference between high-frequency circuit boards and ordinary circuit boards? Comprehensive analysis of advantages and disadvantages!

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The frequency circuit board has a higher operating frequency and lower signal distortion rate, but the manufacturing cost is higher and the manufacturing is more difficult. Ordinary circuit boards are relatively low-cost and simple to manufacture, but they cannot meet the working requirements of high-frequency circuits. This article comprehensively explains the differences and characteristics of these two circuit boards through comparisons in technical principles, material differences, design standards, manufacturing difficulty and other aspects.

1. Technical principles

The main difference between high-frequency circuit boards and ordinary circuit boards lies in the processing of electrical signals. In high-frequency circuits, the frequency of electronic signals exceeds 1MHz. At this time, the signal has extremely high frequency and transient response speed. Ordinary circuits can process low-frequency signals and process electrical signals in the range below 1MHz. Because the signal processing requirements of high-frequency circuits are more stringent, circuit boards equipped with high-frequency circuits are endowed with special capabilities such as high interconnection and low noise. Therefore, in order to ensure the normal operation of high-frequency circuit boards, high-frequency circuit boards need to have higher design and manufacturing standards.

2. Material differences

High-frequency circuit boards must be made of high-quality materials to meet their high-speed transmission-related properties. High-frequency circuit boards usually use silicone resin or PTFE (polytetrafluoroethylene) as the substrate material. In contrast, ordinary circuit boards generally use fiberglass, epoxy boards or multi-layer boards as the substrate materials. Among high-frequency materials, silicone and PTFE have the characteristics of lower performance loss, good high-frequency dielectric properties and excellent mechanical strength, while glass fiber and epoxy do not have such superior properties.

3. Design standards

The design standards of high-frequency circuit boards are relatively high, and it is necessary to fully consider the influence of the size of the circuit board, the position of the components and the board structure. In the PCB design of high-frequency circuit boards, design factors such as circuit trace width, line spacing, interlayer secants, no long ground and distributed capacitance need to be considered. Therefore, please note that great care must be taken during the design development of high-frequency circuit boards to ensure the reliability and quality of their functionality.

4. Manufacturing difficulty

The manufacturing of high-frequency circuit boards requires the use of more complex processing, production and testing equipment, with higher manufacturing standards and technical requirements. Factors such as narrow circuit traces and apertures, higher precision, and concise circuits make high-frequency circuit boards more difficult to manufacture and the manufacturing cost is relatively high. But once these requirements are met, more accurate results and lower signal distortion rates can be achieved.

High-frequency circuit boards have higher operating frequencies and lower signal distortion rates, so they are suitable for products in the fields of high-speed communications, wireless communications, and high-frequency applications. At the same time, the manufacturing cost of high-frequency circuit boards is relatively high, and the design is also difficult. Ordinary circuit boards are relatively low-cost and simple to manufacture, but they cannot meet the working requirements of high-frequency circuits, so they can only be used in applications with lower operating frequencies.

Revealing the safety processes and guarantees in aircraft circuit board manufacturing!

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As an important component of aircraft circuit boards, the safety during their manufacturing process is of utmost importance. Through strict processes and safeguards, we can ensure reliable quality and stable performance of circuit boards, thereby ensuring flight safety.

1. Raw material selection and management
The first step in aircraft circuit board manufacturing is raw material selection and management. The most basic raw material for circuit boards is the printed circuit board substrate, and its quality directly affects the performance of the entire circuit board. When selecting a substrate material, factors such as its conductive properties, insulation properties, high temperature resistance, and chemical stability need to be considered to ensure the stability and reliability of the circuit board in different environments. In addition, we must pay attention to the compliance of raw materials and follow relevant national and industry standards and regulations to ensure the safety of circuit boards.

2. Manufacturing process and quality control
During the manufacturing process of aircraft circuit boards, a series of processes and quality control requirements need to be strictly followed. This includes design, plate making, printing, curing, electroplating, assembly and other links. Each link has corresponding process requirements and inspection standards to ensure that each step complies with specifications and eliminate possible defects and failures. For example, during the plate making process, it is necessary to ensure the accuracy and consistency of the drawings to avoid failures caused by design errors on the circuit board. In the electroplating process, the concentration and temperature of the plating solution need to be controlled to ensure the uniformity and adhesion of the metal layer.

3.Quality inspection and testing
Quality inspection and testing are important aspects to ensure the quality of aircraft circuit boards. After manufacturing is complete, the circuit board needs to undergo comprehensive quality inspection and testing to verify its performance and reliability. This includes visual inspection, dimensional measurement, electrical performance testing, reliability testing and many other aspects. Through these inspections and tests, potential defects and problems can be discovered, and repairs and adjustments can be made in a timely manner to ensure that the circuit board meets the design requirements and meets the performance and safety requirements related to the aircraft.

4. Traceability and management system
During the manufacturing process of aircraft circuit boards, a complete traceability and management system needs to be established. This includes effective traceability and management of raw materials, process parameters, quality records and other information. Through the traceability and management system, the entire manufacturing process can be recorded for subsequent follow-up and problem tracing. This is of great significance for discovering and solving potential problems and improving the quality and reliability of circuit board manufacturing.

Through the effective use and implementation of raw material selection and management, manufacturing process and quality control, quality inspection and testing, and traceability and management systems, the reliable quality and stable performance of aircraft circuit boards can be ensured. This not only ensures flight safety, but also provides reliable technical support for the normal operation of the aircraft. Therefore, in the manufacturing of aircraft circuit boards, great attention should be paid to the implementation of safety processes and guarantees, and continuous optimization and improvement should be made to ensure that every link of casting flight trust is effectively guaranteed.

What are the three-proof standards for aerospace circuit boards?

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Aerospace circuit boards are one of the important components in the aerospace industry. This article will comprehensively analyze the three-proof standards for aerospace circuit boards, namely moisture-proof, salt spray-proof, and mildew-proof. Implementation of these standards is critical to ensuring flight safety. The reasonable design and implementation of moisture-proof, salt-spray-proof, and mildew-proof measures can greatly improve the stability and reliability of circuit boards, thereby ensuring the normal operation of the aircraft.

1. Moisture-proof
Moisture resistance is an important issue that must be considered in the design of aerospace circuit boards. In a humid environment, circuit boards are easily corroded by moisture, leading to reduced performance of electronic components and even short-circuit failures. Therefore, it is necessary to take a series of moisture-proof measures to protect the circuit board. This includes selecting materials with good moisture-proof properties to manufacture circuit boards, such as high-performance glass fiber reinforced materials and plastic films that can effectively isolate moisture. Secondly, encapsulate the circuit board and use encapsulation materials with good moisture-proof properties, such as epoxy resin, etc. In addition, temperature and humidity must be strictly controlled during the welding process to reduce the impact of moisture on the circuit board.

2. Anti-salt spray
Aerospace circuit boards often need to work in marine environments or areas containing salt spray, and salt spray is very corrosive to circuit boards. Therefore, preventing salt spray corrosion has become one of the essential considerations in circuit board design. In order to improve the salt spray resistance of circuit boards, protective coating technology can be used. This coating is usually an epoxy resin or polyurethane material, which can effectively prevent salt spray from corroding circuit boards. At the same time, choosing metals with good corrosion resistance for connectors, lines and other components of circuit boards can delay the damage to circuit boards caused by salt spray. In addition, regular maintenance and cleaning to ensure that there are no salt spray deposits on the surface of the circuit board is also one of the effective measures to protect the circuit board.

3. Anti-mildew
In high-humidity environments, aerospace circuit boards are susceptible to mold attack, resulting in circuit board performance degradation or failure. Therefore, mildew prevention is an important part of ensuring long-term reliable operation of circuit boards. Make your circuit boards by choosing mildew-resistant materials. Such as using substrate materials with antifungal properties and antifungal agents. During production and storage, maintain appropriate temperature and humidity to avoid mold growth caused by excessive humidity. In addition, pay attention to the sealing performance of the circuit board to ensure that there are no cracks and holes to prevent mold from entering.

The three-proof standards for aerospace circuit boards, namely moisture-proof, salt-spray-proof and mildew-proof, play an important role in ensuring flight safety. By selecting materials with good moisture-proof properties, encapsulation processing, protective coating technology and other measures, the stability and reliability of the circuit board can be improved, allowing it to operate normally in harsh environments such as moisture, salt spray, and high humidity. The implementation of these measures requires strict quality control and maintenance plans to ensure that the circuit board can continue to work stably and provide reliable guarantee for flight.

Accurate to the point, super cost-effective! Medical circuit board customization price revealed!

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Medical circuit board customization is one of the key links in the field of medical equipment. It embodies the requirements of precision and the pursuit of ultra-high cost performance. With the continuous development of medical technology, electronic components are increasingly used in medical equipment, and the price and quality of customized circuit boards directly affect the performance and reliability of medical equipment. This article will delve into the price of medical circuit board customization and elaborate on it from four aspects: cost, design, quality and market demand.

1. Cost control
The price of medical circuit board customization is first subject to cost factors. The procurement of electronic components, PCB manufacturing, patch welding, testing and inspection will all incur certain costs. Among them, the procurement of electronic components is an important part. The prices of components of different specifications, brands and quality levels vary greatly. The cost of equipment, labor and materials required in the manufacturing and assembly process also have an impact on the final price. Therefore, when customizing medical circuit boards, effective cost control is the key to ensuring reasonable prices.

2. Design requirements
Medical circuit board customization requires precision because the stability and reliability of medical equipment are crucial to the safety of patients. Design engineers need to carefully design circuit boards based on different medical equipment needs to ensure the stability and performance of each functional module. The complexity and technical requirements of the design will directly affect the price of medical circuit boards. At the same time, factors such as circuit board layout, heat dissipation, and EMC also need to be considered during the design stage to ensure the normal operation of medical equipment.

3. Quality Assurance
As a core component of medical equipment, medical circuit boards have particularly important quality requirements. During the production process, a strict quality management system needs to be followed to ensure product reliability and stability. This includes quality selection of parts, quality control of production lines, and environmental electrostatic protection. Through strict quality inspection and reliability testing, we ensure the quality of medical circuit boards and achieve long-term stable operation. However, in order to meet high-quality requirements, more costs are required for medical circuit board customization.

4. Market demand
The price of medical circuit board customization is also affected by market demand. The medical equipment market is highly competitive, and different manufacturers have different needs for product customization. Large medical equipment requires more complex circuit board design and higher quality assurance, so customization prices will be relatively high. The requirements for circuit boards for small medical equipment may be relatively simple, and the customization price is relatively low. At the same time, the market demand for medical circuit boards with special functions and high performance will also affect the price of customization.

The price of medical circuit board customization is affected by multiple factors. When customizing medical circuit boards, manufacturers need to fully consider these factors and, while meeting performance and quality requirements, try to control costs to provide products with ultra-high cost performance. Only in this way can the customized price of medical circuit boards truly meet market demand and play its important role in medical equipment.
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Differences between PCB positive and negative film processes.

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PCB positive and negative films are two important steps in the PCB manufacturing process, and there are some differences between them. Below we will explore the flow of these two processes and their differences in detail.

First, let’s understand the concepts of positive and negative films. In PCB manufacturing, the photolithography process mainly involves the production of photographic plates. The positive film is usually used to make the copper layer pattern of the PCB, while the negative film is used to make the solder mask, character logo and other patterns of the PCB.

Feature film process:

1. Design drawing: First, use CAD software to make drawings according to the PCB design drawings, including wiring, component installation locations, solder mask areas, etc.

2. Make negatives: Convert the drawings into negatives suitable for PCB production, usually using translucent film for printing.

3. Prepare photosensitive coating: In order to allow the pattern on the negative film to be transferred to the PCB material, a layer of photosensitive coating needs to be applied to the PCB material.

4. Exposure and development: Place the negative film on the PCB material coated with photosensitive agent, and transfer the pattern on the negative film to the PCB material through the exposure machine. Then, the exposed PCB material is developed to remove the unexposed portion of the photosensitive coating, leaving the exposed portion.

5. Corrosion: Use chemicals to corrode the developed PCB material to remove the copper layer in the exposed area, leaving only wiring, pads and other required circuits.

6. Cleaning: Clean the corroded PCB to remove residual photosensitizer and corrosive agent.

7. Solder mask and character marking: According to the PCB design requirements, the PCB is processed with solder mask and character marking.

Negative process:

1. Design and drawing: Just like the positive film, you first need to design and draw, including patterns such as solder mask and character logos.

2. Make negatives: Convert the designed drawings into negatives suitable for PCB production.

3. Prepare the negative film: Place the negative film on a piece of ordinary negative film, and fit the two negative films together to ensure accurate positioning.

4. Exposure and development: Place the negative film on the PCB material coated with photosensitizer, and transfer the pattern on the negative film to the PCB material through the exposure machine. Then, the exposed PCB material is developed to remove the unexposed portion of the photosensitive coating, leaving the exposed portion.

5. Corrosion: Use chemicals to corrode the developed PCB material to remove the copper layer in the unexposed areas, leaving only wiring, pads and other required circuits.

6. Cleaning: Clean the corroded PCB to remove residual photosensitizer and corrosive agent.

7. Solder mask and character marking: According to the PCB design requirements, the PCB is processed with solder mask and character marking.

The main difference between the positive and negative processes is the way the negative is made and the direction in which the pattern is transferred during the exposure process. In the positive film process, making negatives is to directly convert the designed drawings into negatives suitable for PCB production. In the negative film process, a negative film needs to be made first, then laminated to an ordinary film, and the pattern on the negative film is transferred to the PCB material through exposure.

In addition, other steps in the positive and negative processes, such as preparing the photosensitive coating, developing, etching, cleaning, soldering mask and character marking, are the same.

To sum up, the process differences between positive films and negative films in the PCB manufacturing process are mainly reflected in the way of making negative films and the direction of pattern transfer during the exposure process. Positive film is to directly convert the designed drawings into negative film, while negative film requires making a negative film and laminating it with ordinary negative film. Other steps such as photosensitization, development, etching, cleaning and solder mask are the same. The difference between these two processes allows them to achieve different pattern requirements of PCB, thereby meeting different PCB design needs.

Refined PCB design of low-power DC-DC power module.

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1）1. Introduction to DC-DC power supply applications

1. Introduction to DC-DC application types

DC-DC power supply is the core device for DC voltage conversion, including LDO and other types. Among them, devices implemented using switching methods are often called DC-DC converters. This type of power supply has the advantages of low power consumption, high efficiency, small size, light weight, high reliability, anti-interference, and wide range output, so it is widely used in the electronic field.

 

2.Working principle of DC-DC power supply

The working principle of DC-DC power supply involves voltage conversion and regulation. This process is mainly realized through the converter of switching power supply. The DC-DC converter is responsible for converting the input DC voltage into the required output DC voltage in the switching power supply. In general, the working principle of this converter can be divided into three main steps:

1) Filtering: When the mains power is turned on through the input switch, it first becomes pulsating DC through the rectifier circuit, and then filters out the ripples through the filter circuit, turning it into smooth DC, which is supplied to the converter for conversion.

2) Conversion: The DC-DC converter generates a certain pulse power from the input voltage through the power switch tube and energy storage inductor, and then uses the pulse transformer and rectifier filter circuit to obtain the corresponding output voltage. The voltage conversion is achieved by controlling the switching timing of the switching tube through PWM (Pulse Width Modulation) or PFM (Frequency Modulation). In the switching power supply, the switching speed of the switching tube is very fast, and the switching action is generally completed within tens of microseconds. This speed is much faster than the adjustment speed of the traditional linear power supply.

3) Regulation: The stability of the output voltage is achieved through a feedback loop. When the output voltage increases, the sample signal obtained through the sampling resistor will increase. The error signal obtained after comparing this signal with the reference voltage will increase, and then the conduction of the switching tube is reduced through PWM or PFM control. The turn-on time is reduced, thereby reducing the average power output by the converter and achieving stability of the output voltage.
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（2）. Selection of key components

1. Output inductor

The inductor stores magnetic energy to ensure stable current output. When choosing an inductor, you need to weigh the size. Large inductors have small losses but slow response, while small inductors respond quickly but have large losses. Consider the saturation current to ensure the filtering effect.

2. Voltage dividing resistor

The voltage dividing resistors form a voltage dividing network and feed back the output voltage to the control circuit to accurately control the PWM duty cycle and stabilize the output voltage value. Choose high-precision resistors to ensure circuit accuracy.

3. Input capacitor

When selecting the input capacitor, consider the equivalent inductance and self-resonant frequency. Capacitors with large capacitance filter out low-frequency noise, and capacitors with small capacitance filter out high-frequency noise. Combination and parallel use can achieve excellent filtering effect, stabilize the input voltage and filter out AC components.

4. Output capacitor

The output capacitor filters out switching ripple and ensures pure output current. The larger the capacitance, the smaller the impedance and the easier it is for ripples to flow through. Choosing the appropriate output capacitor is critical to the stable operation of the circuit.

 

When selecting these core components, we need to consider various factors to achieve the best balance. For example, the selection of the inductor requires a balance between efficiency and response speed; the voltage divider resistor needs to accurately and stably feedback the voltage; the input and output capacitors need to be selected according to different operating frequency noise characteristics; and the final output capacitor needs to be Consider capacitance and ESR to minimize ripple. Through careful selection, we can make the circuit work in an efficient and stable state, thereby maximizing the performance of the circuit.

（3）DC-DC power supply layout and wiring recommendations

For power module layout and wiring, you can download the chip’s datasheet in advance and design according to the recommended layout and wiring.

1. Layout design
1) Chip power supply proximity principle: For the switching power supply that provides voltage to the chip, ensure that it is placed as close to the chip as possible. This prevents low-voltage output lines from being too long, thereby reducing voltage drop and ensuring that power supply performance is not affected.

2) Avoid electromagnetic interference: Switching power supplies work under high voltage and large current conditions, which may cause complex electromagnetic compatibility issues. Therefore, sensitive components should be avoided around the switching power supply to reduce the impact of electromagnetic interference on the work of the components.

3) Layout with the power supply chip as the core: During layout, the switching power supply chip should be organized as the core component. The input and output ends of the power filter should be laid out to ensure sufficient distance to prevent noise from coupling from the input end to the output end. Components should be arranged neatly and compactly on the PCB to reduce and shorten the leads and connections between components.
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2. Wiring design
1) Avoid parallel wires: The wires used at the input and output ends should avoid adjacent parallel wires as much as possible to reduce unnecessary electromagnetic interference.

2) Thick ground wire: Thickening the ground wire between the input and output can ensure stable current and reduce feedback coupling.

3) Handling of high-current leads: High-current leads, such as public ground wires, power input/output wires, etc., should be made as thick as possible. This can reduce wiring resistance and voltage drop, thereby reducing self-excitation caused by parasitic coupling.

 

3. Heat dissipation considerations
1) Heat dissipation ground area: Since the heat dissipation of the switching power supply is relatively large, the area of the heat dissipation ground (copper) should be increased as much as possible to ensure effective heat dissipation.

2) Large-area copper laying and drilling: The input and output ends should be laid with copper over a large area and drilled with as many holes as possible. This can not only meet the current requirements, but also help improve the heat dissipation effect.