Wave soldering is an integral part of the mixed-technology Printed Circuit Board (PCB) assembly process. Due to the higher melting points of lead-free alloys as compared to eutectic SnPb solder, a narrower process window needs to be used for the wave soldering process. Inadequate solder temperature can impact solder joint yields with an increasing number of component and board related defects. The temperature of the molten solder used during wave soldering is critical to maintain adequate capillary action as the PCB traverses across the solder wave, good capillary action helps to achieve good hole fill for through hole devices. One way to improve this process is to increase the operating temperature of the molten wave. However, this increase could result in the thermal disintegration of surface mount or through hole devices, board discoloration and warpage. For 'thick' (0.125" and above) PCBs, another option is to control the speed of the conveyor used to transport these boards over the wave of molten solder. This paper focuses on determining the process parameters for wave soldering 'thick' PCBs using lead-free solder material. The objective of this research was to determine the appropriate process window for the lead-free wave soldering of 0.125" thick PCBs with Ni/Au surface finish. The lead-free solder used was 95.5%Sn, 3.8%Ag, and 0.7% Cu (SAC387) in conjunction with a Volatile Organic Compound (VOC) free, no-clean, water based flux. Experiments were designed using statistical principles. Four factors that have a critical impact on solder joint formation were considered: solder pot temperature, conveyor speed, top side pre-heat temperature, and wave RPM. Each factor had three levels and a Taguchi L9 orthogonal array was used as the experimental matrix. Complete (100%) inspection was carried out using X-ray laminography equipment to determine top side wetting, percentage of hole fill, bridging, flux residue, and solder balling. The results demonstrated that a higher solder pot temperature resulted in fewer defects and a slower conveyor speed enhanced holefill but increased other defects, such as bridging.
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