RE>Intrusive Reflow                          2/23/96

Liam,
We've been using intrusive reflow (paste in hole) techniques for 3-4 years with success.  To my knowledge, there isn't a published IPC or other standard (although the good folks from IPC will correct this in a hurry if I'm wrong!).
 
Our assembly suppliers generally use two stencils:  the first has just the component hole locations to force the paste into the holes, while the second contains oversized apertures for the component holes in addition to SMT pads.  

While this strategy tends to provide us with a lot of solder paste in the holes, keep in mind that the final volume of solder is roughly half that of the solder paste.  From our tests and from what I've read in the literature, this is sufficient, but it doesn't meet some Workmanship Standards for topside fillet formation (like IPC-A-610).  We've had no problems convincing our customers of reliability, although we had to modify our internal Workmanship Standards.

Good luck,
Greg Bartlett
Mercury Computer Systems
Chelmsford, MA
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Are many companies using intrusive reflow ? Does anybody know if there is a 
   published IPC standard on implementing this technology , particularly in 
relation to design guidelines, recommended stencil thicknesses etc.

Thanks,

Liam Brown
AMT Ireland
University of Limerick
National Technological Park
Plassey
Limerick
Ireland
Tel:      353-61-331588
Fax:     353-61-330316
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