For high-reliability automotive PCBs, how to ensure that products meet the requirements is the goal pursued by many PCB manufacturers. In the production control, some reliability testing problems are prone to insufficient performance, which needs to be analyzed and used as a reference for the industry.
1. High and low temperature cycle test.
Power control systems and brake control systems use automotive PCBs. The design and process require higher reliability. For example, automotive control systems usually require 500 high and low temperature cycles, and individual key components even require up to 2000 high and low temperature cycles.
A. High and low temperature cycle test conditions and requirements. Low temperature to high temperature: -40c-125℃, conversion time: 10s, duration after reaching the highest (low) temperature: 15min, interconnection resistance change rate <10% (some customers require <5%).
B. Improvement direction. The cracks appearing in the slices after high and low temperature have a great relationship with the Tg value of the plate, the quality of the drilling, and the etchback before PTH. The material selection must be done to reduce the two-axis expansion of the plate thickness. ,
Three different types of pads (phenolic pads, wooden pads and melamine pads) were used for drilling experiments. After drilling, the SEM was used to observe the sludge on the hole wall. The results showed that the phenolic pads were used for sludge on both sides of the hole wall. Relatively more; when using wooden backing plates, there is more sludge on one side of the hole wall and little sludge on the other side; when using melamine backing plates, the drilling sludge is evenly distributed on the hole wall, and the amount of sludge is relatively small.
3. Etching. With different etchback methods, the amount of etchback on the hole wall will be somewhat different. How to effectively remove epoxy drilling dirt, ensure that the hole wall roughness meets the requirements and reduce the wicking effect is a headache for many PCB manufacturers. Because the roughness of the hole wall is too large, it will cause blowing holes during welding and the coating fracture during high and low temperature cycles; a large wicking effect may cause electromigration between holes and forming short circuits; if the amount of etchback is controlled relatively small , There may be cracks in the joints after high and low temperature cycles.
4. Electromigration problem: In the high temperature and high humidity environment, due to the existence of the galvanic battery phenomenon, the PCB may appear electromigration phenomenon (also called electro-corrosion), which will cause the insulation resistance between the insulators to continue to decrease over time, even Secondary hazards such as short circuit, heat generation and fire of parts occur. Therefore, car manufacturers are paying more and more attention to this aspect.