Jorge,

Solder balls at Wave Solder are caused by:

    * Moisture in PCB laminate
    * Poor /Porous copper plating in PTH

When PCB hits wave solder, rise in temperature causes the moisture to
blow off as steam  coming through the PTH copper plating voids. If you
cross section the PTH that shows indication of solder balls, you can
verify the presence of plating voids. You may also cross section as
received PCB to establish PTH quality.

Assembly process changes will have minimal affect on solder balls. Your
PCB supplier has to provide void free copper in PTH to eliminate solder
balls at wave solder.

If it is a few holes per board, you may use Water Soluble Tape to mask
the PTH.. The tape will be cleaned off during warm water rinse section
of cleaning process.

You can contact me off line for use of water soluble tape and technical
requirements for the process if you so wish.




Jorge Rodriguez wrote:

>Technetters,
>
>        My company is having a solder ball problem on the wave solder. The
>issue is primarily caused by overly large un-masked  vias on both sides. The
>via diameter is 25 mils with an annular ring of 25 mils on a .062"  board.
>On the wave solder process, the flux gets entrapped inside the vias and no
>matter what we do on the pre-heating section there still flux remaining
>inside that causes the solder to explode into tiny solder balls when it gets
>to the laminar section of the wave, like a volcano effect on the component
>side. These boards have also a good amount of the same vias under fine pitch
>QFP devices , this narrows our process window  if we want to heat the board
>even more. Heating the board more on the preheaters to resolve the solder
>ball problem leads on re-reflowing of the leads of those devices and quality
>problems as a result of that, the QFP pins pop up and become un-soldered.
>The customer does not want to use smaller vias or get them masked off since
>vias are used for test and rework purposes, they want to be able to insert
>wires inside the vias in case they need to change the board configuration.
>Any ideas on what to do with the wave process to resolve this issue?
>
>
>        Any ideas would be greatly appreciated.
>
>
>
>Jorge Rodriguez
>Process Engineer
>Varian Electronics Manufacturing
>615 South River Drive
>Tempe, AZ 85281
>Phone: (480) 968-6790 X 4258
>Fax: (480) 829-4000
>E-mail: [log in to unmask]
>
>---------------------------------------------------------------------------------
>Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
>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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
>To recieve ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
>Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
>Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
>information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
>---------------------------------------------------------------------------------
>

--
_________________________
pratap singh
tel/fax: 512-255-6820
email: [log in to unmask]
WEB: www.rampinc.com