Technet,



I have come across a rash of failed assemblies that have 0805 capacitors

and resistors, bottom side glued, wave soldered and washed. Trouble

shooter reported touching up the solder joints on a few areas and the

boards would pass test.



I had a look at one board which was reported to have a 0805 56K resistor

with "drifting" values. I pulled the component off mechanically in order

not to apply any heat and noticed several mini-voids within the adhesive

body. I have seen solder bridge within the glue before but this was the

first time I saw wet residue within the voids.



You can view a sample image from Steve's web site:

http://www.stevezeva.homestead.com/files/SMTAdhesive.jpg



The image showed the bottom side of the cracked resistor after removal

(white), with a portion of solder mask (green) and SMT adhesive (red).



I used a 8mil stencil. The thermal profile was verified and conformed to

the slope/ curing specs.



Has anyone seen this before? Any explanation as to how the void was

formed and how moisture got tapped in? Does anyone re-use their glue on

the line or throw away any left-over to avoid moisture in the glue?







Rgds,

Peter



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