Try pre-form solder instead of solder paste. Of course, process controls of flux still a key parameter. Vacuum oven will further reduce the issue. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro Sent: Friday, 18 February 2011 12:27 AM To: [log in to unmask] Subject: Re: [TN] Voids issue on Aluminium base plate Cedric, Lots of things come to mind....plating thicknesses, paste patterns, wetting, profiles. Is there any pattern to the voiding? Does it resemble the printed paste shape? I have soldered lots of RF transistor bases down, but I haven't ever soldered them to NiAg plated aluminum (always to Ni/Au plated copper slugs). You don't mention the paste patterns used but that will contribute to large voiding if you don't give the gases a path to get out. I would reduce the solder paste coverage to 45%, use a checkerboard pattern of dots, and then observe the voiding pattern. This assumes that the voiding is not relative to wetting as that will change everything. To do this, check the solderability of both surfaces being soldered to independently. Phil -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Cedric ORAIN Sent: Thursday, February 17, 2011 6:26 AM To: [log in to unmask] Subject: [TN] Voids issue on Aluminium base plate Dear Technetters, We have to solder a RF power transistor onto an aluminium base plate and we are facing with a very challenging issue. We encountered a high voids rate (>30% or 40%) underneath the component body (which is about 35x10mm). This is not acceptable for this application. The component is Nickel/gold plated whereas the aluminium baseplate is plated with Nickel and Silver and then cleaned with solvent. We tried to change/adapt: - soak time of the profile, - 2 difference solder pastes (SAC305), - change the screen design and thickness Finally none of these parameters looks to have significant effect on voids rate. We are now wondering if the solderability of the Ni/Ag plating is good enough and even if it is convenient for that purpose. Is somebody could give us advises? How to enhanced NiAg plating solderability (acid ?!, ...)? Which flux could help to compensate the poor wettability? Which kind of plating would be preferable? ... Thanks and regards, Cedric ------------------------------------------------------------------------ ------ This message and any attachments are solely for the use of the addressee and may contain L-3 proprietary information that may also be defined as USG export controlled technical data. If you are not the intended recipient, any disclosure, use or distribution of its content is prohibited. Please notify the sender by reply e-mail and immediately delete this message and any attachments. ______________________________________________________________________ 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 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 -----------------------------------------------------