A quick and dirty technique is to reflow the solder paste into a bump or slight convex surface on the both surfaces, inspect the solder then if the solder is good put a very light film of solder gel on either each surface or one of the surfaces depending on the density of the flux gel at reflow temperature...
The stand the components vertically and reflow the assembly...
The convex surfaces will be touching in the middle as you progress toward reflow temperatures. As the more heat is applied the melts merge forming a solid melt zone from the center of the joint moving outward as the convex surfaces collapse into the melt...This will sweep the gas, fluids and debris that creates voids out of the joint... This technique will only work if you can expose the components to more than one "reflow cycle". This works great in all applications where the components can take the cycle... Have done this with prototype and production PCAs... Remember solder bumping PCAs?
This may not prevent voiding due to surface metal de-wetting or material entrapment in the base materials due to surface finish mechanical and chemical prep processes...
Paul
Paul Edwards
Process/Quality Engineering
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Friday, February 18, 2011 3:36 AM
To: [log in to unmask]
Subject: Re: [TN] Voids issue on Aluminium base plate
Cedric
I echo Inge's comments with respect to 'drying' the elements and George,
Richard and Paul's on the possibilities of volatiles and suggested use of
pre-tinning and minimal flux. Definitely Denny's on wetting to the Ni.
Since you are seeing lot to lot differences - the first thing I would
attempt is to pre-tin! Answer your Ni wetting question once and for all.
By pre-tinning, you should be able to force it to wett! ... then clean it.
The channels which Paul mentions DO work, and don't have to be extremely
macroscopic... but you likely can not do that with these parts.
Somewhat surprised that no one commented on Thorsten's suggestion for
(vacuum) vapor phase reflow.
I my days of making power devices I had the luxury of a vacuum
reflow/brazing system using conduction heating via graphite tooling. You
would be surprised at how much 'gas & crap' [technical terms] you can pull
out of a plated metal under vacuum - to Inge's comment. Having pre-wetted
components and no flux [could purge with a forming gas] and ability to
over-pressurize would result in essentially void free joints.
I can see that the vapor phase approach could drastically lessen/eliminate
the need for a flux - assuming the surfaces are clean. I realize you don't
have one, but maybe for this project, you could go to someone that does -
depending upon whether this was a one shot deal, or will be a recurring
project/nightmare.
What I am not familiar with however, is .... is there such a thing as a
vacuum vapor phase??
How does that work, or was that just a 'typo'?
I would like to learn more about that particular piece of equipment if there
is such a critter.
Sincerely,
Steve Creswick
http://www.linkedin.com/in/stevencreswick
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
==============================================================================
This email and any attachments thereto may contain private, confidential, and
privileged material for the sole use of the intended recipient. Any review, copying,
or distribution of this email (or any attachments thereto) by others is strictly prohibited.
If you are not the intended recipient, please contact [log in to unmask]
immediately and permanently delete the original and any copies of this email and
any attachments thereto.
==============================================================================
______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
---------------------------------------------------
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.aspx?Pageid=E-mail-Forums for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
