Heat resistance refers to the ability of PCB resistance to heat and mechanical stress in the welding process, and the mechanism of PCB in heat resistance test is generally included in the following:
1) test samples of different materials in the temperature change, the expansion and contraction of different performance and internal thermal mechanical stress in the sample, resulting in the generation of cracks and delamination.
2) test samples inside the micro defects (including holes, micro cracks, etc.), is the thermal mechanical stress concentration, the role of the amplifier to play the role of. Under the action of the internal stress of the sample, more easily lead to the generation of cracks or delamination.
3) in the test sample volatile compounds, including volatile organic compounds and water, in the high temperature and rapid temperature change, the rapid expansion produce huge internal steam pressure, when the expansion of the steam pressure reach small defects in the inside of the test samples (including empty, micro cracks, micro defects corresponding to the amplifier function will lead to delamination.
The HDI plate is easy to be layered on top of the dense buried holes, which is caused by the special structure of the HDI plate in the area of the pore distribution. The stress analysis of the buried hole area is shown in table 1. Without buried hole region (structure 1) in the thermal expansion of the heat resistance test, on the same plane Z direction of each position of the expansion are uniform, and therefore there will be no due to differences in the structure of the stress concentration region. When the region in the design of buried hole and buried holes are drilled on the substrate surface (2), buried in a hole and buried hole between the A-A section, due to substrate did not receive the buried hole in the Z direction constraint and expansion large amount, and in buried vias and pads where B-B section on, because the substrate by buried hole in the Z direction constraint and expansion quantity is small and the amount of swelling of the differences, in buried hole welding disc and HDI medium and plugging resin junction and nearby areas caused by stress concentration, and thus more likely to form cracks and delamination.
The HDI board easily at the bottom of the outer copper surface delamination, which is due to the mount and welding, heating PCB, rapid expansion of volatile matter (including volatile organic compounds and water), outer surface copper block volatile substances (including volatile organic compounds and water) in time to escape, resulting in huge internal steam pressure, when the expansion of the steam pressure reach small defects in the inside of the test samples (including empty, micro cracks, micro defects correspond to the amplifier function will lead to delamination.