Our experience and testing with Ion Chromotography and SIR show that by
using an RMA flux and Semiaqueous cleaner (in particular Qualitek 730 paste,
Kester 185 liquid flux,  and Axarel 38 cleaning solution) the residues,
while present, are not detrimental to the performance. This has been
supported by 10's, if not hundred's of thousands of units in the field, in
outdoor environments throughout the world with no known corrosion problems.
In general we do NOT conformally coat our boards. In fact, we have just
about satisfied our only customer that requires it, that it is not
necessary.

By the way some of our ceramic disc antennas are approximately 2 inches in
diameter and sit flush on the board - we also use a 6 mil stencil.

Hope this helps - If you want to contact me off line I would be glad to go
into more detail.
REGARDS
Sherman Banks
[log in to unmask]
408/481-6047



> -----Original Message-----
> From: VOLPE, RAY [SMTP:[log in to unmask]]
> Sent: Monday, June 21, 1999 6:49 AM
> To:   [log in to unmask]
> 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