> >question regarding plated closed vias: I have the same concern Paul just >mentioned. Is there not a reliability concern with trapped contaminants in >the via when plating closed? I stopped spec-ing minus tol same as via dia. >because of this. Yes. Been there, done that, got the t-shirt. However, there are some very few fabs now who've managed to adapt the new-fangled filled copper uVia processes (e.g. Shipley's uFill) to fill small thru vias completely and reliably. >Happy 2010, >-Chris > > > > > > "Brooks, Bill" > <[log in to unmask] > > To > Sent by: TechNet [log in to unmask] > <[log in to unmask]> cc > > Subject > 01/04/2010 02:47 Re: [TN] Thermally Conductive & > PM Plated Via Fill > > > Please respond to > TechNet E-Mail > Forum > <[log in to unmask]> > ; Please respond > to > "Brooks, Bill" > <[log in to unmask] > > > > > > > > > >Randy, > >There are some things that defy logic and reason... and are often done >without the proper science. I'm sure there are many reasons 'why'. I >won't try to guess at them. Do you remember soldermask over solder >plated finish for double sided boards and what that produced? A real >mess after the board was heated to solder the parts... but board >manufacturers did it anyway... because it was on the print... go >figure... > >Tin/lead solder is a poor conductor of heat compared to copper... So in >thermal applications we increase the thickness of the via barrel from >1oz to 2-3oz copper to get better thermal conductivity through the vias >to the back side of the board where we can put a thermal pad to the >chassis if needed. > >Some folks don't think beyond the transfer of heat to the board... and >forget to make a path for that heat to the ambient air... which is a >mistake they will discover later when they test the unit over temp. Just >pumping heat into the board is not always a complete solution. Depending >upon thermal transfer thru solder filled vias doesn't make sense either. > >Solder filling of exposed thermal vias that are in large 'belly pad' >designs is really unavoidable at assembly but not a significant or >useful part of the equation for thermal transfer... > >The cross sectional area of that copper is modeled for thermal >applications. The more copper the better for conductivity. We use very >small diameter via thru holes and allow them to plate shut if possible. >Whatever solder gets into them is incidental not intentional. Solid >copper plating thru the board would be the best condition... but it >costs more. So far we have not had any problems with this current design >concept The small diameter vias tend to rob less solder from the belly >pad producing a partially filled via due to the capillary action of the >solder... we typically use solder with lead in it... lead free solder >may not wick into the holes quite so easily as it has a different >surface tension. > >The idea of 'plugging vias with solder' as a pre-assembly step seems >unwise to me too for the logical reasons you have already presented. > >I will be curious to hear any arguments to the contrary... > >Best regards, > >Bill Brooks | Datron World Communications, Inc. >PCB Designer/Engineer | Office: 760-602-7004| Fax: 760-597-3777 | >[log in to unmask] >1808 Aston Avenue, Suite 230, Carlsbad, CA 92008 | www.dtwc.com > >Performance You Require. Value You ExpectTM > >-----Original Message----- >From: TechNet [mailto:[log in to unmask]] On Behalf Of Randy >Sent: Monday, January 04, 2010 7:56 AM >To: [log in to unmask] >Subject: Re: [TN] Thermally Conductive & Plated Via Fill > >Can someone please help me break my paradigm with "filling vias in >process with solder"? I have difficulty seeing how this works. How do >you ensure consistent, predictable solder fill in thermal vias during >assembly? If inconsistent, then you really can't count on it to be >there >since any time it's not there you'll pay for it. > >If by some chance you can get solder to fill all vias completely, then >how do you avoid solder flowing out the opposite end of the vias? >Protruding solder "bumps" can interfere with solder paste printing if >bottom (second) side assembly is required. These solder "bumps" can >also interfere with heat sinking if intimate contact is required in this > >area for heat dissipation. > >Regards, >Randy > > >On Tue, 29 Dec 2009 12:28:35 -0800, Dwight Mattix ><[log in to unmask]> wrote: > > >Practically speaking, using "thermal conductive" and "CB100" in the > >same sentence is an oxymoron. > > > > > >Cu ~= 300 w/mK > >Solder, Ormet, et al ~= 25 w/mk > >CB100 ~=3 w/mK > > > >Small amount more annular copper, filling with Ormet paste (not a > >cheaper option though) or filling via in process with solder yields > >much greater increase in thermal conductivity than CB100. > > > >At 11:55 AM 12/29/2009, Joe Lara wrote: > >>Hello TechNetter's, > >> > >>Im currently using Du Ponts "CB-100" Conductive Paste to vill Vias > >>at $400 per 100G. Is > >>there a more affordable way of filling vias that call out to be > >>filled (thermal conductive) and > >>plated? > >> > >> > >>Best Regards, > >> > >>Joe > >> > >--------------------------------------------------- >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 >----------------------------------------------------- > > > > > > >This e-mail message is intended only for the use of the intended recipient(s). >The information contained therein may be confidential or privileged, >and its disclosure or reproduction is strictly prohibited. >If you are not the intended recipient, please return it immediately >to its sender at the above address and destroy it. > > > >--------------------------------------------------- >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 -----------------------------------------------------