Michael,

It is possible that you may be seeing a solder mask “scum” which acts a
barrier and prevents solder from wetting that particular area. You will see
this in both horizontal and vertical HASL processes.  This is typically
caused in the solder mask developing operation and due to poor developer
equipment cleaning and maintenance.

Have your supplier first check for plugged nozzles in the developer and
subsequent spray rinse. Also, see if they clean their solder mask developer
routinely (weekly) with an equipment cleaner. And finally, have your
supplier contact their vendor(s), supplying developer solution and solder
mask, and have them perform an audit on their processes.

Hope this helps you.

Michael Newman
Sr. Process Engineer



>From: "McMonagle, Michael R." <[log in to unmask]>
>Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>,        "McMonagle,
>Michael R." <[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] Exposed Copper on Fabs
>Date: Tue, 2 Nov 1999 13:27:49 -0600
>
>         I need a little insight from those of you in the fab end of the
>industry regarding an issue we have seen on a few incoming fabs. They are
>processed by the supplier using a horizontal HASL process, and we are
>finding random instances of partially or fully exposed copper on pads.
>Meaning, you may have one pad out of a row of a QFP pattern or one pad out
>of an entire BGA array that is bare copper even though all
>adjacent/surrounding pads are fully covered with HASL. Is this something
>inherent in the horizontal HASL process? If so, what is the phenomena that
>causes it? If not horizontal HASL processing, what are other potential
>causes? I have my ideas, but am looking for others. Enquiring minds want to
>know....
>
>Mike McMonagle
>PCA Process Engineering Supervisor
>K*Tec Electronics
>1111 Gillingham Lane
>Sugar Land, TX  77478
>(281) 243-5639 Phone
>(281) 243-5539 Fax
>[log in to unmask]
>
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