Ray,

As I remember there was a most interesting and relevant article that
appeared in the February or March issue of Precision Cleaning magazine.

It was written by some poor sole at Lockheed Martin who evidently
experienced similar problems. It was something like: Cleaning of LCC
devices.

I know it is an American publication and that their web site is (I Think!):
http://www.precisioncleaning.com

Sorry to be so vague, but I can't find my copy. If I do I will let you know.

Regards,
Graham Naisbitt

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Concoat Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK

Tel: +44 (0) 1276 691100  Fax: +44 (0) 1276 691227
----- Original Message -----
From: VOLPE, RAY <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, June 21, 1999 2:49 PM
Subject: [TN] Cleanliness Problem


> Fellow TechNetters:
>
> I have a ceramic resonator surface mounted on a (Type 1) FR-4 PCB in a
> Class 2 application. The flush pads (gold flash plated) on the underside
> of the component have castellations similar ta an LCC. There is almost
> no component to PCB surface clearance. We are using an .008 mil stencil
> to apply the solder paste then reflow solder.  We believe the
> insufficient clearance under this part is limiting the cleaning
> solutions ability to adequately flush the solder residues from under the
> part. We have had failures due to residue trapped beneath this
> component. When the component was removed and cleaned underneath then
> resoldered to the board at a rework station, the part would function
> normally. I am looking for, and would very much appreciate some success
> stories on similar parts or ideas to fix this problem. We can not comply
> to J-STD-001 as required,  because we can not demonstrate satisfactory
> cleaning.
>
> Some inhouse suggestions have been:
> *       Increase stencil thickness (raise part)
> *       Drill holes under part in PCB (no board, no entrapment)
>
> Any validity to these ideas ?
>
> Thanks in advance,
>
> Ray Volpe
> [log in to unmask]
> (609) 583-9400  x286
>