What issues should be noted when designing medical grade circuit boards

The design of medical grade circuit boards should focus on the following key issues:

1. Compliance with regulations and standards

It is necessary to strictly comply with international regulations such as ISO 13485 (Quality Management System for Medical Devices), IEC 60601-1 (Safety Standard for Medical Electrical Equipment), FDA 21 CFR Part 820, etc., to ensure that product design meets the functional, performance, and safety requirements of medical devices.

2. Material and process selection

Substrate: FR-4 materials with high heat resistance and low coefficient of thermal expansion (CTE) or metal substrates (such as aluminum substrates) are preferred to ensure long-term stability.

Cleanliness control: Manufacturing must comply with IPC-5704 standards, with ion contamination ≤ 1.56 μ g/cm ², particle residue ≤ 50/cm ² (≥ 5 μ m), and implantable devices must be in a sterile state (≤ 1 CFU/cm ²).

3. Signal and Electromagnetic Protection

Impedance matching: By accurately calculating the transmission line width and interlayer spacing, impedance matching of 50 Ω or 100 Ω can be achieved, and differential wiring is preferred to reduce interference.

Shielding and isolation: Adding shielding layers or isolation devices to sensitive signal lines, designing multi-layer PCBs with dedicated power/ground planes to reduce electromagnetic radiation.

4. Compatibility between Biology and Chemistry

Contact safety: Devices that come into direct contact with the human body, such as wearable monitoring devices, must meet strict requirements for leakage distance and electrical clearance.

Material selection: Implantable devices are made of medical grade polyimide materials that have undergone biocompatibility testing to avoid the release of harmful substances.

5. Low power design

For portable devices such as blood glucose meters, it is necessary to optimize the MCU and power management chip, shorten the wiring length to reduce parasitic capacitance, and design a low impedance power network to reduce losses.

6. Manufacturability design

Following the IPC Class 3 standard, optimize wiring to avoid sharp corners and overly dense routing, maintain appropriate line width and spacing to reduce manufacturing defects.

What are the precautions for medical electronic PCBA manufacturing?

1、 Design phase

1. Compliance with regulations and standards: The PCBA design of medical devices must strictly comply with international and regional regulations and standards, such as ISO13485, IEC60601, FDA's 21CFR 820, etc., to ensure that the product design meets the functional, performance requirements, and safety standards of medical devices, in order to pass relevant certifications and ensure that the product is legally marketed.

2. Material selection:

PCB board materials: Common materials include FR-4, metal substrates (such as aluminum substrates), and ceramic substrates. These materials need to have high thermal stability, good mechanical strength, and corrosion resistance to adapt to extreme environments such as high temperature and humidity that medical equipment may face.

3. Components and solder paste: Components must meet the quality requirements of medical devices, with accurate information such as model, specifications, polarity, etc; The solder paste should ensure that it can evenly cover the solder pads during the soldering process, avoiding the phenomenon of insufficient solder and missed brushing, and the amount of solder paste should be moderate to prevent welding defects caused by too much or too little.

4. Hierarchical structure and wiring design: Reasonable hierarchical structure and wiring design can effectively reduce signal interference, improve circuit stability and reliability. For complex medical equipment, using multi-layer PCB boards to distribute different functional modules at different levels is an effective way to improve anti-interference ability. Design document preparation: Prepare complete design documents, including circuit schematics, PCB layout diagrams, and BOM (Bill of Materials), use professional EDA tools for circuit design and PCB layout, and ensure the rationality and feasibility of the design.

2、 Manufacturing process

1. PCB manufacturing accuracy and environmental control:

Manufacturing process: The main processes of PCB manufacturing include cutting, forming, copper plating, drilling, yellow light typesetting, etching, etc. High precision equipment and rigorous process control are required to ensure PCB quality and avoid minor deviations affecting subsequent SMT and soldering effects.

Environmental conditions: The PCB manufacturing process needs to be carried out in a dust-free and anti-static environment to prevent dust and static electricity from affecting the circuit board, ensuring the cleanliness and electrical performance of the PCB board.

SMT surface mount processing:

SMT accuracy and speed: High precision SMT machines are used to achieve precise component installation, with errors controlled within 0.01mm, while pursuing appropriate high-speed operation to improve production efficiency.

Solder paste selection and printing: Choose the appropriate solder paste based on the characteristics of the components. Solder paste printing should ensure uniform and accurate coverage of PCB pads, laying a good foundation for soldering.

Reflow soldering and temperature control: By controlling the temperature curve of the exhaust furnace, it is ensured that the solder paste is fully melted to form a reliable connection. A suitable temperature curve can ensure soldering quality, reduce soldering defects and defective products. AOI inspection and quality control: Automatic optical inspection (AOI) technology is used to visually inspect the welded PCB board, promptly detect welding defects or errors, and then manually retest to ensure that the solder joints and components meet quality standards.

DIP plug-in processing: For components that cannot be mounted through SMT technology, such as large connectors, electrolytic capacitors, etc., DIP plug-in processing is used, including plug-in, wave soldering, and manual repair soldering. The accuracy of the plug-in and the reliability of the soldering must be strictly controlled.

3、 Quality control

1. Quality control of electronic components:

Avoid counterfeit components: Establish a strict procurement process, screen and audit suppliers rigorously, and ensure that components come from legitimate channels; Strengthen the construction of quality inspection departments, strictly inspect incoming components, and establish a random sampling system; Implement outdated management strategies to avoid the use of outdated and unauthorized components; Strengthen employee training and enhance awareness of identifying and preventing counterfeit components.

Testing and screening: Before conducting PCBA sampling, professional testing equipment and technology are used to conduct electrical performance testing, environmental adaptability testing, etc. on the components, and qualified components are screened for manufacturing.

Welding quality control: Strictly control the welding quality, and use automatic welding equipment and technology to ensure the consistency and reliability of welding. Check and evaluate the welding quality, and promptly discover and solve problems. The solder joints should be smooth and free of burrs, with solder exceeding 2/3 of the height of the solder joint, and there should be no cracking of the solder joint section. Functional testing and debugging:

Functional testing: After completing welding and assembly, rigorous functional testing such as ICT testing, FCT testing, and aging testing is conducted to identify potential faults and hazards.

Debugging and program burning: Debug the PCBA according to device requirements, check the working status of each component, and ensure that the equipment runs as expected; If necessary, burn the corresponding program to enable the device to have intelligent control function.

2. Cleaning, coating, and packaging:

Cleaning and coating: Clean after processing to remove residual flux and other pollutants during the welding process; Coating on the surface of PCB to form a protective film, preventing environmental factors such as moisture and corrosion from affecting the circuit.

Packaging and Transportation: Conduct final inspection, including visual inspection, performance testing, and safety checks, to ensure that the product meets the specified standards and requirements. After passing the inspection, package the product properly to protect it from damage during transportation and storage.

4、 Other aspects

Cleanliness and anti-static control: Strictly control cleanliness during the production process to remove possible residual through holes or surface stains during welding; Take effective anti-static measures, such as setting grounding wires and using anti-static coatings, to prevent potential damage to BGA and IC components caused by static electricity.

Environmental adaptability testing: High end medical electronic equipment needs to operate in various environments, so it is necessary to conduct environmental adaptability testing on the circuit board, including temperature range, humidity range, electromagnetic compatibility, etc., to ensure the stability and reliability of the circuit board in various environments.