Don, I don't know if there is a formal standard but as a customer I
would reject boards with this kind of variation.  First the 80 microinch
end is so thin that it will be mostly a tin/copper intermetallic.  This
will be bad for solderability.  Second will be pasting problems,
especially for fine pitch parts.  The high points will lift the stencil
off the board and cause poor gasketing allowing paste to leak under the
stencil at nearby low points. High points on a QFP pattern will also
cause poor paste release on low points because of reduced surface
tension.  This will result in unsoldered leads, weak joints and
bridging.  My recommendation would be 100 microinches minimum (short
shelf life), 300 microinches ideal + - 100.  Tilting won't be a problem
when the solder melts.

>-----Original Message-----
>From:  Don Karp [SMTP:[log in to unmask]]
>Sent:  Wednesday, July 21, 1999 5:56 AM
>To:    [log in to unmask]
>Subject:       [TN] HASL co-planarity
>
>Hello All,
>
>I've been asked a stumper (for me anyway).
>
>Is there a specification for the co-planarity (?) of HASL across the board?
>My customer is concerned that thickness variations (80 microinches on one
>land / 800 microinches on the other land - for the same component) are
>causing tilting of his components.
>
>I know that there are minimum thickness requirements which address
>solderability, but have not heard of the above.
>
>Don Karp
>Trace Laboratories - Central << File: ATT00819.html >>

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