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March 1999

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Sat, 6 Mar 1999 09:21:42 -0600
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I'm having a fun time between BGA rework/repair using an SRT 1000 and SPC efforts (much easier)
using DEK stencil printing processes and BTU reflow with 6 Fuji lines in between.

Concerning the BGA stuff, I'm getting about 60% success using this rework capability as being able
to remove, place, and reflow 432 perimeter BGA's and others. This is unacceptable. I can remove or
place and reflow two parts in sequence while the third does not budge or reflow all around the
perimeter.

This situation is most perplexing. Wow, I said that! Has anyone else had similar experiences with
this phenomonon (I said something like it again)?

I have used both Conceptronic and Pace's high end machines before. They seemed flawless doing
similar repairs to lesser boards - as 8 layers compared with the 16's here.

My primary concern is the bottom side heater at 750 watts and three elements relying on "hot" air
"blanketing" the board's bottom surface though many device edges are very close to the board's edges
(.100" or less) and other design rule violations. This does not allow the "blanket" to provide the
same temperatures. I see T/C recorded deltas in excess of 30 degrees on dummies and a little less on
"real" boards.

I am keying on part removal success with outside T/C's attached closely to part corners to ensure I
start out low in the reflow sequence. This allows two more passes to reflow before scrapping $2500
boards. Anyway, is there anyone capable of offering objective suggestions concerning this type
behaviour.

Earl Moon

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