Barry,
Not sure of your reason for not simply doing a standard glue/place/wave, but
here are some thoughts:
1) When you add paste to this process you will be adding cost, stencil cost,
printer set-up and paste cost (albeit small, if this is a volume product it
could add-up).
2) We have done bottomside paste/glue/place/wave, but the reason for this
was driven by some high-profile/heavy parts that were difficult to
mount/retain on the board. But keep in mind the smaller the parts, the more
difficult it is to control this process.
3)If using standard IPC SOT-23 and 0805 pads designed for wave solder, with
paste, there is a risk of the glue dot size (.030"?)
interfering/touching/contaminating the solder paste.
4) When you paste AND glue, if you have an insufficient glue condition under
a part, the residual tack of the solder paste can mask the fact that the
part is not glued down sufficiently. Then when the board reaches wave, the
part may fall off. Where-as, if there were no solder paste the part would
have fallen off earlier, this would be identified as a process glue problem
that could be addressed before the entire run was completed.
Hope this helps. Feel free to call Mark or myself if you would like to
discuss this matter a little more.
Mark Spitnale/Jeff Hempton
At 03:19 PM 6/5/97 EDT, you wrote:
>Hi Technetters,
>
>Given design: 2 sided mixed SMT/Thru-hole board. Top is all SMT. Bottom
(wave
>side) has approx:
> 12 SOIC-14
> 5 SOIC-8
> 20 SOT-23
> 10 each of Tantalum A, B, C case sizes
> Predominantly 0805 R's and C's
> A few 1206 R's and C's
> (of course) Leads from 10 thru-hole components to be wave soldered on the
>bottom
>SMT pad geometry is standard IPC. SMT and Wave process is "No Clean"
>
>Would you:
> A. Glue bottom SMTs (no paste) to be wave soldered later, or,
> B. Redundantly apply paste (still with glue) and reflow the bottom SMTs,
>before wave solder?
>
>Comments explaining your choice, or any technical reference on this matter,
>would be much appreciated.
>
>Thanks and good day to all.
>
>Barry Khor
>Sr. Staff Specialist, Quality Eng.
>Hughes Network Systems
>San Diego, CA
>
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----------------------------------
Jeff L. Hempton phone: (219) 429-7335 Fax: (219) 429-4688
Boardshop Manufacturing Engineer Mail Stop: 25-31
Hughes Defense Communications
1010 Production Road, Fort Wayne, IN 46808-4106
Email: [log in to unmask]
"The man who rolls up his sleeves seldom loses his shirt."--Thomas Cowan
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