Solution to crack defect appearing between copper layers in PCB during heat treatment
[Introduction]As the communication products develop towards high frequency,high speed,and high density,the via-in-pad plating over(VIPPO)process has been widely adopted in the manufacturing of printed circuit board(PCB).However,these PCBs are susceptible to cracking between over Cu coating and bottom Cu coating during lead-free soldering,resulting in product failure.The present study was conducted to address this issue by heat treatment.[Method]The pretreated plug-in resin and board resin for PCB were subjected to heat treatment at 120 ℃,followed by reflowing at 260 ℃ to simulate the high-temperature soldering process.The coefficient of thermal expansion(CET)and glass transition temperature(Tg)of the two kinds of resins after heat treatment under different conditions and being reflowed for different times were measured.The mass loss of the resins after heat treatment for different time were analyzed.The cracking between different Cu coatings after reflowing was observed by scanning electron microscopy(SEM).[Result]The CET values of plug-in resin and board resin were greatly decreased after heat treatment,and their glass transition temperatures were also optimized.No crack was found between over Cu coating and bottom Cu coating at the corner of microvia on heat-treated PCB after 6 cycles of reflow.[Conclusion]The failure of PCB products caused by the cracking between different Cu coatings can be effectively mitigated by heat treatment after resin plugging and cover plating,respectively.
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