Advanced Packaging Technology Conference Proceedings


LEAD-FREE SN3.5AG AND SN0.7CU WAVE SOLDER EVALUATION WITH VOC-FREE NO-CLEAN AND WATER SOLUBLE FLUXES

Author: Jasbir Bath
Company: Solectron Corporation
Date Published: 6/12/2001   Conference: Advanced Packaging Technology


Abstract: Two lead-free solders (Sn3.5Ag, Sn0.7Cu) were evaluated in terms of solderability and holefill thickness. The evaluation was performed on a Solectron Wave Soldering Test Vehicle using a VOC-free no-clean and a water-soluble flux on a production wave soldering machine. The process parameters varied in the Design of Experiment were solder pot temperature, conveyor speed, preheat temperature and nitrogen flow rate over the wave. The assembled component boards were evaluated by visual as well as X-ray laminography inspection to determine holefill and solderability and compared with control tin-lead wave soldered boards. Optimized process parameters for the 4 lead-free solder/ flux combinations were determined and confirmation runs were performed on OSP coated, NiAu and tin-lead HASL finish boards.

Cross-sections of various through-hole components soldered using the lead-free solders showed reduced holefill compared to those soldered with tin-lead solder. This was particularly the case whenno-clean flux was used. In some instances soldering defects such as fillet lifting on tin-lead HASL coated boards were observed. Mechanical pull test data was also reviewed for SOIC and chip joints wave soldered using lead-free and tin-lead solders. Temperatures were determined on certain components on the board during the wave soldering operation with the lead-free solders. The temperatures used with the lead-free solders were slightly higher than those used presently for tin-lead.

Keywords: lead-free, Sn3.5Ag, Sn0.7Cu, Sn37Pb, VOC-free flux, no-clean flux, water-soluble flux, wave soldering, solderability, visual defects, holefill, X-ray laminography, microstructure, fillet lifting, pull tests, shear tests, thermal cycling, temperature profiling, flux deposition, drossing, HASL, NiAu, OSP, impurity levels.



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