we have a issue of post-reflow oven (SMT) soldering defects of blowholes and pinholes. Any suggestions or knowledge on root cause is appreciated to be share?
we DI water wash and oven bake the PCB bareboards at 90deg-C for 60mins, to remove possible dust, volatiles and also thermal condition the PCB (polymide).
The reflow oven profile plotting shows the profile to be within specs for the "supplier recommended specs".
Preheat between 150-180degC is average 60-75sec.
Reflow above 183degC is average 45sec.
Ramp is 1.7degC/sec.
Peak reflow temp averages 208degC max.
The component solder fillet affected is a MLF.
we control the environment to be 22-26degC at 40-60RH%.
post-reflow inspection shows blowholes at solder areas near to the base of the PCB pad. Although it also manifests as a violent explosion appearance the the top of the solder fillet region.
post-reflow inspection also shows pinhole in solder areas random in the solder fillets.
we tried to increase reflow time, it appears to reduce the occurence of blowhole, and marginal helps in the pinhole reduction. Any ideas how to further eliminate the pinholes?
we did try increasing the reflow peak temperature to average 215-218degC, but that just increased the rate of blowholes.
Appreciate any ideas or suggestions, on how to eliminate this blowhole and pinhole issue. Thanks in advance!