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April 2015 • SMT Magazine 25 halogen-free versus halogen-containing—does not appear to have a significant impact. Conclusions There are many variables that affect SIR performance. And with the specific knowledge of the impact of proper heating on a flux's SIR performance, such an experiment as this seemed appropriate. What was surprising is that even with a very short "soak" the SIR per- formance of a residue can be "improved" more than by using a higher peak temperature. Such knowledge could be useful in such problem- atic situations as temperature sensitive assem- blies and flux residues trapped under compo- nent bodies and RF shields. The latter situa- tions can produce unusual visual anomalies and gooey flux residues, as was discovered in a prior work, with less than optimum SIR perfor- mance. As the acumen of knowledge increases relative to the parameters which affect SIR per- formance of flux residues, no-clean processes can be honed to provide reliable products. For those processes involving cleaning/removal of no-clean residues, especially with the ever decreasing standoff of SMT components, more work should be done to understand the im- pact of partial or incomplete removal of such residues. SMT Originally published in the IPC APEX EXPO 2014 proceedings. references 1. IPC J-STD-004: Requirement for Soldering Fluxes. 2. E. Bastow, The Effects of Partially Activat- ed No-Clean Flux Residues Under Component Bodies and No-Clean Flux Residues Entrapped Under RF Cans on Electrical Reliability, IPC APEX EXPO 2011 conference. Figure 29: Halogen-containing normalized average SIR values. eric bastow is assistant technical manager for indium corporation and a certified ipc-a-600 and 610d specialist. ElECTriCal rEliaBiliTy OF NO-ClEaN SOlDEr paSTE Flux rESiDuES continues FeAture

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