Gabi ,
3 basic possibities for such shadows :
1 ) Catalyst ( Palladium ) adsorbed on epoxy causing initiation of Nickel
plating followed by Gold
2 ) Unproper rinsing during plating process causing drag-out of chemistry in
concaves around pads .
3 ) Less likely , but still possible : residues of unetched basic copper
arround circuitry .


Best regards from Cyla and Boaz . Call us if You need any assistance with
examination of such boards .
Edward


At 22:11 10/06/98 +0300, you wrote:
>Hello, TechNetters!
>Some questions about electrolessNi/Au plated circuits:
>What is the cause of shadow plating between the pad and the surrounding
>solder mask?
>Is it acceptable by IPC standards for Class2,3 if it extends to 30% of
>the distance between the
>fine pitch lands separated by ~4mil solder mask?
>It seems that the presence of the solder mask near the plating area
>enhances the occurrence of
>the phenomenon.
>Also, we see differences in the appearance of the fine pitch area
>between two different manufacturers.
>One of them gives us very clearly defined pads without any shadowing ,
>the other-shadow plating
>along the long edges of the pads, for the same artwork.
>We are concerned about violating the IPC requirements ,about the
>necessity of solder mask
>between the pads with less than 20mil pitch and about shorts after
>reflow soldering.
>Please answer me as soon as possible.
>Thank you in advance for your help,
>Gaby
>
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Edward Szpruch
Eltek Ltd - Israel
Tel  972 3 9395050
Fax 972 3 9309581
E-mail :  [log in to unmask]

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