Yes,

     My experience with Lifted fiducial pads can be attributed to one of
     the following:

     1. The angle at which the panel/board is fed through the HAL,
        especially prominent with depanelized boards versus paneled.

     2. Since you are using a HAL, you are more than likely to be running
        panels at a 45 degree angle to obtain a coplanar surface.  Doing
        so, will require the edges of the board to make contact with the
        tin rollers first, in turn applying localized preassure over the
        fiducials/corner versus equalizing the roller preassure over the
        span of the panel.

     3. Item 2 worsens the issues further should you use copper foils of
        1oz (seldom) and greater (2oz, very likely).  The etch factor or
        undercut that is associate with thicker copper weakens the
        ficucial.  SMT Lands don't experience this problem due to the
        copper to laminate interface being greater.

     4. Adjust the tin roller spacing.  I somethimes found operators
        running .093 or .125 thick boards through .062 set opening.  The
        Rollers need to be adjusted for the amount of copper weight in
        addition to overall PCB thickness'.

     5. More importantly is how many thermal excursions has this board gone
        through.  The solder pot temperature is typically 500F+-10.
        If the first HASL is unsuccessful, allow the panel to cool before
        processing again.  Running the panels multiple times to close to
        the Tg allows for material degradation, thus weakening the
        copper to laminate interface and possible removal of the laminate
        buttercoat.

     Hope this helps,

     John Gulley
     Inet
     1255 W. 15th St.
     Plano, TX 75075














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Subject: [TECHNET] Lifted Fiducials
Author:  Ron Hayashi <[log in to unmask]> at Internet