I'm got a materials application question that I hope some of the experts on TechNet might help me come up with a solution. We have had a problem with MELFs during reflow and some 0805 and 0508 chip components tombstoning.  Some of it is related to pad design I'm trying to come up with a quick fix until I can get some design changed.  Normally I would add some SMT chipbonder / SMT adhesive under the parts and cure while the paste is being reflowed. However, since this material is not on the Bill of Material, I cannot add this without each customer approving this addition.


Does anyone have any experience with  any recommendations for a temporary water soluble staking material that could be machine dispensed and would be compatible with a SMT process?.  I am trying to find a water soluble material that I could dispense with either one of the two  Camalot dispensing systems we have in house.  I would like a material that  would be cured in the preheat portion of the reflow profile and serve to hold the part in place during the reflow portion of the reflow profile. The material would then be washed off during the subsequent de-fluxing in-line washing operation (we use a heated saponified wash process)


The other idea I was playing around was to  use the existing non-clay based water soluble masking material, Alpha 110 water soluble mask. With a slow enough ramp, the material does not expand and does adequately hold parts in place. The problem is that the material is too thin to dispense and hold the necessary dot profile. I really need a thixotropic material. In the past, I have used a product from Cabot Chemicals called Cab-O-Sil. It is an inert fused silica material that I have added as an inert filler to thicken material to increase viscosity. Most of the clay based materials seem to swell up when I try to cure in the preheat/soak parts of a reflow profile.

Any ideas would be appreciated.

Thanks
Tom



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