Tom,
What I see in the picture is, that there is no metallisation under the
head of the component.
Did you do the coagulation test?:
  stick 2 stickers onto each other, punch a hole in the stack with a
perforator and stick the stack on an alumina substrate, Fill the
cavity with solder paste, remove the stack and reflow the substrate on
liquid solder. There are no satellites allowed around the formed
solder ball.

Peer Langeveld
Consultant Soft Soldering Processes
5502 VH 8 The Netherlands



2007/10/12, Steve Gregory <[log in to unmask]>:
> Hi Tom!
>
> Got your picture posted. It's at:
>
> http://stevezeva.homestead.com/files/1206_SolderBall.JPG
>
> What kind of soldermask is on the board? LPI or dryfilm? Do you have the
> mask relieved around the pads by a few mils?
>
> I ask that because it almost looks like the solderball is caught right
> at the edge of the mask sort of...
>
> Steve Gregory
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gervascio, Thomas
> Sent: Friday, October 12, 2007 1:38 PM
> To: [log in to unmask]
> Subject: [TN] Small solder balls
>
> Has anyone ever established a baseline of the anticipated frequency of
> solder balls under chip components? We are doing Space assembly work and
> the specifications allow for no solder balls. We are using a ROL0 solder
> paste and cleaning in an inline semi-aqueous cleaner with
> saponification. What is being rejected are solder balls about a 1-2 mils
> in diameter that are intermittently trapped under low profile chip caps
> and resistors. I suspect it is an agglomeration of solder particles in
> the paste occurring during reflow. I have tried all the usual things-
> stencil aperture modifications: - homeplates; reverse homeplates(like a
> bowtie design that reduced the printed pad by 25%); homeplates which are
> offset 7 mils from the inside edge of the pad: tried reducing hot slump
> of the paste (changed from 90sec soak between 150-170 sec (per vendor
> recommendations) to ramp to spike; tried reducing placement force or
> fudging part thickness.
>
> What I am experience I believe is typical of the process but would like
> some input from my peers.
>
> Steve Gregory, can I post a photo on your website- stevezeva.com to show
> what I am talking about?
>
> Thanks
>
> Tom Gervascio
>
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0 To
> unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
> (re-start) delivery of Technet send e-mail to [log in to unmask]: SET
> Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the
> posts: send e-mail to [log in to unmask]: SET Technet Digest Search the
> archives of previous posts at: http://listserv.ipc.org/archives Please
> visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for
> additional information, or contact Keach Sasamori at [log in to unmask] or
> 847-615-7100 ext.2815
> -----------------------------------------------------
>
> ---------------------------------------------------
> Technet Mail List provided as a service by IPC using LISTSERV 15.0
> To unsubscribe, send a message to [log in to unmask] with following text in
> the BODY (NOT the subject field): SIGNOFF Technet
> To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
> To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
> Search the archives of previous posts at: http://listserv.ipc.org/archives
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
> -----------------------------------------------------
>

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------