Good morning,
Problem definition Poor soldering of thermistors with Ag/Pd termination
Background Process: lead free reflow soldering Paste type: Multicore LF300, SAC305 Component type: 0805 chip thermistor, Ag/Pd termination PWB finish: immersion Ag Reflow profile: fits LF300 process window
Defect photo http://download.yousendit.com/AC1B758D6E715940
This problem has appeared at PWB populated mostly with simple chips and a few IC�s. PWB is thin (0.8mm) and evenly populated so there are no any temperature gradients across the PWB during heating. During soldering stage all solder flows to component�s lead leaving soldering evidence on PWB�s pad (please refer to the picture). Solder melts and flows. But flows mainly to component�s lead. Resulting joint appearance is cold one. The rest of PWB is absolutely fine. No any soldering anomalies.
According to component manufacturer requirements components have to be soldered within one year after shipment. Reels I checked were out of date. Could it cause such soldering anomalies? Is it possible to sort this issue out with process adjustment (profile tweaking etc.)?
By the way, manual rework of this defect after reflow is extremely hard. What could it be?
BR, Pavel
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