SMTA China Conference Proceedings

Process Considerations in Reducing Voiding in High Reliability Lead Free Solder Joints

Authors: Steve Brown, Mitch Holtzer, Gilbert Renaud (presented by William Yu)
Company: Alpha
Date Published: 4/21/2015   Conference: SMTA China

Abstract: This paper is in English and Chinese languages.

With the increasing transition of European and American automotive OEMs to ROHS compliant soldering materials, high reliability tin/silver/copper alloys have been widely examined. One six part alloy known as Innolot has become widely adapted because of its high resistance to thermal cycle fatigue and resistance to high temperature creep.

Examining data from numerous field trials has shown that solder pastes using Innolot alloy tend to produce more voids in bottom terminated components (BTCs) when compared to the same paste flux vehicle used with SAC 305 alloy. Several techniques have been reported for reducing voids in BGA components, but many of these techniques do not seem to reduce voiding when Innolot solder paste is used in conjunction with BTCs.

Video data showing the formation of voids in a simulated BTC reflow process led to the development of a different type of reflow profile strategy. Data mining of field reports indicated that this strategy had worked several times without the need to reflow the solder joint under vacuum. A controlled experiment using five different reflow profiles and a previously used BTC voiding test vehicle was undertaken to validate the field observations. This paper will show the field data and the results of the controlled experiments, giving the reader a new reflow strategy for reducing BTC voids when using Innolot based solder paste.

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