PCB Tech - Important features of high-reliability PCB

Regardless of the quality and reliability of the PCB just produced, there is not much difference on the surface of the PCB. However, it is through the surface that experienced engineers see the differences, and these design differences are critical to the durability and functionality of the PCB. Whether in the manufacturing process or in actual use, the most important thing is that the PCB must have reliable performance. In addition to cost factors, PCB defects are likely to cause defects in the final product during the assembly process. Product failure may occur during use. Therefore, it is no exaggeration to say that the cost of a high-quality PCB is negligible. In market segments, especially in the market for products in key application areas, the consequences of PCB failures are disastrous.

When comparing PCB prices and determining PCB manufacturers, comparisons should be made from the following aspects to ensure product quality. Although the cost of reliable, guaranteed and long-life products is higher than that of ordinary products, in the long run, the stability and durability of the products cannot be easily saved. The following Lao Chen will introduce the 14 most important features of high-reliability circuit boards:

1. 25 micron hole wall copper thickness

Features that are conducive to reliability: Enhance reliability, including improving the expansion resistance of the z-axis.

Compared with this, other design defects: blow holes or outgassing, electrical connectivity problems during assembly (inner layer separation, hole wall fracture), or failures may occur under load conditions in actual use. IPCClass2 (the standard adopted by most factories) requires 20% less copper plating.

2. No welding repair or open circuit repair

Features conducive to reliability: perfect circuit can ensure reliability and safety, no maintenance, no risk

Compared with this, other design flaws: If improperly repaired, it will cause the circuit board to break. Even if the repair is ‘proper’, there is a risk of failure under load conditions (vibration, etc.), which may cause failure in actual use.

3. Exceeding the cleanliness requirements of IPC specifications

Features conducive to reliability: improving PCB cleanliness can improve reliability.

Compared with this, other design defects: residues and solder accumulation on the circuit board bring risks to the solder mask, and ionic residues can cause corrosion and contamination risks on the soldering surface, which may lead to reliability problems (bad solder joints/electrical Failure), and ultimately increase the probability of actual failure.

4. Strictly control the service life of each surface treatment

Features conducive to reliability: solderability, reliability, and reduce the risk of moisture intrusion

Compared with this, other design defects: due to the metallographic changes in the surface treatment of old circuit boards, soldering problems may occur, and moisture intrusion may cause delamination and internal defects during the assembly process and/or actual use. Layer and hole wall separation (open circuit) and other issues.

5. Use internationally well-known substrates-do not use "local" or unknown brands

Features conducive to reliability: improved reliability and known performance

Compared with this, other design flaws: poor mechanical performance means that the circuit board cannot perform the expected performance under assembly conditions, for example: high expansion performance will cause delamination, disconnection and warpage problems. Weakened electrical characteristics can lead to poor impedance performance.

6. The tolerance of the copper clad laminate meets the requirements of IPC4101ClassB/L

Features conducive to reliability: Strict control of the thickness of the dielectric layer can reduce the deviation of expected electrical performance.

Compared with this, other design defects: the electrical performance may not meet the specified requirements, and the output/performance of the same batch of components will be quite different.

7. Define solder mask materials to ensure compliance with IPC-SM-840ClassT requirements

Features that are conducive to reliability: "Excellent" ink, to achieve ink safety, to ensure that the solder mask ink meets UL standards.

Compared with this, other design flaws: Inferior ink can cause adhesion, flux resistance and hardness problems. All these problems will cause the solder mask to separate from the circuit board and eventually lead to corrosion of the copper circuit. Poor insulation properties can cause short circuits due to accidental electrical continuity/arc.

8. Defining the tolerances of shapes, holes and other mechanical features

Features that are conducive to reliability: Strict tolerance control can improve the dimensional quality of the product-improve fit, shape and function

Compared with this, other design flaws: problems in the assembly process, such as alignment/fitting (only when the assembly is completed will the press-fit pin problem be found). In addition, due to the increased size deviation, there will be problems when installing the base.

9. Requirements for the thickness of the solder mask, although IPC does not have relevant regulations

Features conducive to reliability: improved electrical insulation properties, reduced risk of peeling or loss of adhesion, and enhanced resistance to mechanical impact-no matter where the mechanical impact occurs!

Compared with this, other design defects: thin solder mask can cause adhesion, flux resistance and hardness problems. All these problems will cause the solder mask to separate from the circuit board and eventually lead to corrosion of the copper circuit. Poor insulation properties due to the thin solder mask can cause short circuits due to accidental conduction/arc.

10. Appearance requirements and repair requirements are defined, although IPC does not define

Features that are conducive to reliability: Careful care and carefulness in the manufacturing process create safety.

Compared to this, other design defects: multiple scratches, minor damages, repairs and repairs-the circuit board works but doesn't look good. In addition to the problems that can be seen on the surface, what are the invisible risks, the impact on assembly, and the risks in actual use?

11. Requirements for the depth of the plug hole

Features conducive to reliability: high-quality plug holes will reduce the risk of failure during assembly.

Compared with this, other design defects: the chemical residue in the gold deposit process can remain in the hole with the plug hole not full, which causes problems such as solderability. In addition, there may be tin beads hidden in the holes. During assembly or actual use, the tin beads may splash out and cause a short circuit.

12. Specify the brand and model of peelable blue glue

Features that are conducive to reliability: the designation of peelable blue glue can avoid the use of "local" or cheap brands.

Compared with this, other design flaws: Inferior or cheap peelable glue may foam, melt, crack or solidify like concrete during the assembly process, so that the peelable glue cannot be peeled off/doesn't work.

13. Perform specific approval and ordering procedures for each purchase order

Features that are conducive to reliability: The implementation of this program can ensure that all specifications have been confirmed.

Compared with this, other design defects: If the product specifications are not carefully confirmed, the deviation caused by this may not be discovered until the assembly or the final product, and then it is too late.

14. Do not accept boards with scrapped units

Features conducive to reliability: not using partial assembly can help customers improve efficiency.

Compared with this, other design defects: the boards with defects require special assembly procedures. If it is not clear to mark the scrap unit board (x-out) or not isolate it from the board, it may be possible Assemble this known bad board, thus wasting parts and time. If you master the above experience, you can choose a highly reliable PCB manufacturer.