Jens,
I believe the TechNet archives will have some detail on solder balls. In
general there are a few causes for the formation of solder balls.
Environmental exposure of the paste to moisture, this can be from high
humidity, extended queue times after printing or exposure of below room
temperature paste to room temperature air. (ie paste is below dew point)
Another cause would be oxidation of the solder alloy. This may exist in the
paste or be formed during the reflow process, due to the profile not being
optimized to the flux.
Also just a note solder balls are very small and should not be confused with
solder beads, large coalesced solder found at times at edges of caps and
resistors.
        Feel free to contact me off line for more details.
VBK
Vincent B. Kinol CQE [log in to unmask] <mailto:[log in to unmask]>
Applications Engineer OMG Americas Microbond
Phone 919-544-8090 x298 FAX 919-544-7996


        -----Original Message-----
        From:   [log in to unmask] [SMTP:[log in to unmask]]
        Sent:   Tuesday, January 18, 2000 11:16 PM
        To:     [log in to unmask]
        Subject:        [TN] Reflow soldering >>> Solder balls

        Hi,

        sorry for this basic basic question!
        Are there any resources for the solder balls problem? Where do the
come from and how to prevent them?
        Is there any site for solder defects info ?
        regards
        Jens Behrens

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