Printing on the mask ( not perfectly aligned on the pads) will cause balls.
Also be careful not to confuse solder balls with mid solder chips. This is
an age old rage with QC. One is a process indicator the other is a defect.
Humididty and aperture geometry of the stencil are the two biggest factors
next is reflow profile which is easier to control and maintain.
Dave Chapman
Circuit Service, Inc.

 -----Original Message-----
From:   joyce [mailto:[log in to unmask]]
Sent:   Wednesday, December 11, 2002 10:55 AM
To:     [log in to unmask]
Subject:        Re: [TN] Solder ball causes

Add "temperature of the solder is too high"...jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Francis Sun
>Sent: Wednesday, December 11, 2002 11:00 AM
>To: [log in to unmask]
>Subject: [TN] Solder ball causes
>
>
>Hello,
>
>I would like to compile a list of what may cause solder balls
>to form after reflow for our internal consumption. Can anyone
>add to my limited knowledge on some of the causes that can
>create solder balls? My knowledge is limited and some may not
>be correct. If any are not correct please point them out. If
>there is a comprehensive list available in the public domain,
>it would be great if someone can point me in the general
>direction of where it is located.
>
>
>Some of the causes that I sort of know of:   !! BE WARNED !!
>some or all
>may not be correct. :
>
>Moisture from substrate and components
>Dry solder paste
>Wet solder paste?
>Stencil aperture(s) too big
>Wrong pad geometries
>Poor mixing of solder paste
>Solder did not reach room temperatures?
>Solder paste passed shelf life?
>Environment to humidity?
>insufficient heat
>Dwell time under liqudius is too long?
>Dwell time under liqudious is too short?
>Time interval too long between solder application and reflow?
>
>Any help is appreciated.
>
>
> Happy Holidays to all
>
>Francis Sun
>MARK IV Industries
>(905) 624-3025 ext. 1235
>Fax: (905) 624-4572
>
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