In my past I have found that pumice scrubbing
eliminated a similar problem, indicating that it was a
residue that was insoluble, and impervious to chemical
attack. (cured soldermask) Are residues being
deposited during the SM cure cycle? By poor handling?
In a poorly ventilated oven?
--- "Wenger, George M (George)" <[log in to unmask]>
wrote:
> Is the copper pad that doesn't coat with solder on
> the bottom or top of the
> board during the HASL operation? I'm not sure but
> my guess is that they may
> be bottom side features. If they are bottom side
> features I might be able
> to give you an explanation
>
> Regards,
> George
> George M. Wenger DMTS
> (609)-639-2769 Office (609)-639-3210 Lab
> Bell Laboraties Princeton, Engineering Research
> Center
> Supply Network Solutions FMA/AQA/RCA Lab
> Po Box 900, Princeton, NJ 085424-0900
> Route 569 Carter Rd., Hopewell, NJ 08525
>
>
>
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Thursday, August 03, 2000 7:37 AM
> To: [log in to unmask]
> Subject: [TN] Copper Pads After HASL
>
>
> Fellow Technetters,
>
> Occasionally we encounter a phenomenon of copper
> pads remaining
> after HASL. The copper pad is always a pad that is
> defined only by
> soldermask on a ground plane area. Usually it is
> square or rectangular and
> from
> .040" to .080" in dimension. Often small writing in
> the mask will also
> remain
> copper.
> We've checked:
> developer; strength, temp, spray pressures,
> rinse pressure, rinse temp
> developed the boards faster, slower, pad side up
> vs. pad side down
>
> We've checked:
> pre clean strength, temp, copper removal, tried
> faster ,slower , two times
> etc.
> new flux , old flux, spiked flux(HCL), longer solder
> dwell
>
> Is it possible that this is caused by the geometry
> of the pad? It creates a
> sort of inground pool with a mask border. Maybe it
> doesn't rinse or develop
> clean or maybe in the leveler it creates a vapor
> barrier that doesn't allow
> the
> solder contact with the copper.
> That job at the Ice Cream stand is looking better
> and better!
>
> Any input appreciated.
>
> Thanks
>
> Brett Austin
> Nationwide Circuits Inc.
>
>
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