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qfp's on backside

Carol Brumfield

#12088

qfp's on backside | 2 April, 1999

Does anybody put QFP's on the backsides of boards? Can they be reflowed without falling off? Do you use adhesive?

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ScottM

#12089

Re: qfp's on backside | 2 April, 1999

| Does anybody put QFP's on the backsides of boards? Can they be reflowed without falling off? Do you use adhesive? | I've seen QFP's on the backside and yes, they need glued prior to reflow - just a couple of drops on the corners.

Scott

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Bob Willis

#12090

Re: qfp's on backside | 2 April, 1999

| Does anybody put QFP's on the backsides of boards? Can they be reflowed without falling off? Do you use adhesive? | Yes you can reflow them upside down either by Double Sided Reflow or by Simultanous Double Sided Reflow. Many Asian companies wave solder the parts on mixed technoogy boards. The limit for wave is 0.025" if you want reasonable yields.

Further information on double and Simultanous reflow si available from the SMTA Office talk to Dave Gommerman.

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Justin Medernach

#12091

Absolutely, no glue, no fuss. | 6 April, 1999

| Does anybody put QFP's on the backsides of boards? Can they be reflowed without falling off? Do you use adhesive? |

I use a double sided reflow process all day, everyday. I've hung QFP240s with embedded heat sinks and they don't fall off. Yeilds are unaffected and the process is very friendly. If you do have components dropping off in reflow, check two things. a.) your air flow in the reflow zones. It could be set too high and the components will be blown from the substrate. b.)the physical mass of the part. Every once in a while, I lose a heavy D-Pak component but that's about it.

Regards, Justin

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Dick Casagrande

#12092

Re: qfp's on backside | 7 April, 1999

| | Does anybody put QFP's on the backsides of boards? Can they be reflowed without falling off? Do you use adhesive? | | | I've seen QFP's on the backside and yes, they need glued prior to reflow - just a couple of drops on the corners. | | Scott | There are several articles on this subject. One was in May 98 issue of SMT titled "Optimize Solder Reflow" by Marc Peo. He gives following info.

Grams per sq.inch must be less than 30 in order to bottom reflow w/o adhesive. He gives sq. inches as "total pad area".

I never used it so can't give you first hand OK but it may be a good guideline

Also see posting by Bob Willis on 7/24/98. Dick

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