EMSNow - NEW WHITE PAPER - Voiding Behavior in Mixed Solder Alloy Systems

EMSNow - NEW WHITE PAPER - Voiding Behavior in Mixed Solder Alloy Systems:

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NEW WHITE PAPER - Voiding Behavior in Mixed Solder Alloy Systems

By Yan Liu, Derrick Herron, Joanna Keck, and Ning-Cheng Lee.

Jun 21, 2013

The voiding behavior of mixed solder alloy systems using a nitrogen reflow atmosphere during BGA assembly was investigated. 

The solder joints were comprised of a combination of Sn62/Pb36/Ag2 (Sn62), Sn63/Pb37 (Sn63), Sn98.5/Ag1/Cu0.5 (SAC105), and Sn96.5/Ag3/Cu0.5 (SAC305) as the solder ball or solder paste, except for the SnPb solder ball, which used lead-free solder pastes. Assembly of each BGA employed a high temperature (HT) profile for lead-free and mixed systems, and a low temperature (LT) profile for mixed and SnPb systems. 

Mixed systems had higher voiding than lead-free systems when reflowed at HT. SnPb systems had a wider voiding range when compared with mixed systems reflowed at LT. Voiding was found to decrease with reduced alloy surface tension; earlier melting of the bottom solder paste; a narrower pasty range; smaller joint overheating; when the top ball remained solid during reflow; and by using flux alone instead of solder paste.

SMTONLINE Surface Tension and Load-Carrying Capacities of Solder

SMTONLINE Surface Tension and Load-Carrying Capacities of Solder: "
Surface Tension and Load-Carrying Capacities of Solder"

Reflow soldering on both sides of a board is standard procedure in the SMT manufacturing process. When the second component side is soldered, the components hang upside-down on the PCB. When the reflow process reaches its peak range, the possibility of remelting previously finished solder joints cannot be ruled out, which leaves the component hanging directly from the molten solder. 

Manufacturers count on the load-carrying capacity of molten solder millions of times a day. Figure 1 shows a component hanging from a drop of solder. Molten solder is entirely capable of bearing considerable component weight.

Read the full article here.


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