Another cause could be soldermask on the pads. A thin film of soldermask
gives the appearance of exposed copper.
Rick Howieson
GTC

>-----Original Message-----
>From:  McMonagle, Michael R. [SMTP:[log in to unmask]]
>Sent:  Tuesday, November 02, 1999 12:28 PM
>To:    [log in to unmask]
>Subject:       [TN] Exposed Copper on Fabs
>
>        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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