John, Way cool! :) It's reassuring to see someone has been down this road and worked the bugs out of the process... Thank you! Do you suppose that thicker plating in the holes would help the situation? Is there a practical limit to how much plating can be added to the barrel of the thermal vias? I'm planning on pumping about 8 watts of heat thru the thermal vias on a high volume RF board I am doing... Best regards, Bill -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Wednesday, October 03, 2007 3:35 PM To: TechNet E-Mail Forum; Brooks,Bill Subject: RE: [TN] Thermal vias and plugging ... I used to work in a place with a very high wattage output amplifier and a thermal paddle. The mechanical guy was so convinced that the solder would just run down the holes that we forced our fabricator to develop a plugging process which was flush with the surface. After much agnst they developed a process that plugged the vias, then the vias where sanded flush so there was no annualar ring at all. Remember this was 10 years ago. So now we have thermal paddles the vias are filled sanded flush with the copper and the hasl covered copper all around. After about 5,000 units we realized that we were getting voids under these thermal pads. Our theory was that yes the via was plugged but there was about 1 to 2 mils of area on top of the via to the edge of the hasl. So we really had these little cups with each via. Our conclusion was that this was trapping air and causing the problem so we started looking for a plate over process. In the meantime a new mechanical guy hired in and took one look at the thing and did some calculations and said you don't need to plug these vias at all. The surface tension will stop the solder from running down the holes. Sure enough we stopped plugging the holes the paste did not run out and all of our soldering problems went away. His calculations were based on the surface area versus the volume of the via cylinder and how close the thermal pad was to the board. I have done a lot of thermal pads and just left the vias open on both sides and have had no problems with runout. But I would imagine every case is different. In our case we were using 12 mil holes in a .062 thick board and it was important that the termal pad was making contact with the paste. But we built about 40,000 units after that with no problems. -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Brooks,Bill Sent: Wednesday, October 03, 2007 11:51 AM To: [log in to unmask] Subject: [TN] Thermal vias and plugging ... Well this is a little different sidetrack but still connected to vias and filling... but if you are attempting to make 'thermal vias'... what is the most reliable and economic way to accomplish it and successfully get the heat out under a part that has a thermal 'belly' pad? The issues I am aware of are related to the solder paste melting into the vias at reflow ... its touchy to do because the vias if left open tend to 'steal' the solder from under the part... sometimes causing insufficient solder in the joint. Are fabricators and designers using a some special compound to fill the vias? Something like loaded thermal epoxy? Is there any data on the subject that I can read? Or someone to talk to that has some experience with the issues? Cost and performance are things we try to balance... especially when the customer buys the 'must work but I don't want to pay that much' option... :) Bill -----Original Message----- From: Ted Tontis [mailto:[log in to unmask]] Sent: Wednesday, October 03, 2007 10:37 AM To: [log in to unmask] Subject: Re: [TN] Via plugging with LPI soldermask... As I understand it you can not use LPI solder resist to plug a via or insure a via is %100 plugged. You have to you some type of filler if you require a via to be plugged. I have seen some of those threads regarding links between conductive epoxy and via barrel failure. Is there any data that suggests that conductive epoxies or fillers shouldn't be used at a specific aspect ratio? What are the chances that the conductive epoxy is increasing hole wall pull away, damaging the barrel? Can non-conductive fillers act as an insulator when it comes to heat transfer within the barrel? Ted -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier Sent: Wednesday, October 03, 2007 11:24 AM To: [log in to unmask] Subject: Re: [TN] Via plugging with LPI soldermask... There is no reason why voids in non-conductive fills in PTVs are a problem. Kim's experience makes sense. Werner -----Original Message----- From: Haynes, Kim <[log in to unmask]> To: [log in to unmask] Sent: Wed, Oct 3 12:12 PM Subject: Re: [TN] Via plugging with LPI soldermask... I hve watched this plug/tent discussion thread with interest. I design and build boards for multi-gigabit transmission rates in a lab environment. When I use conductive filling, I seem to have via problems during thermal cycling device analysis. When I use a non-conductive epoxy, I do not have the problems. I have not been able to prove this hypothesis but I think the conductive fill has a different expansion rate than the board and the small vias tend to crack. The non-conductive epoxy expands at about the same rate as the boards and I do not seem to have the same failure rates from via cracking. One of my board fab shops is mil qual rated and they claim that the govt inspectors do not even want conductive epoxy in the buildings. It makes them nervous because it could be used instead of the non-conductive filler and they do not want any boards with silver epoxy. I have been searching to see if anyone has done controlled tests of conductive epoxy versus non-conductive epoxy fills for via in pad technology. Thanks, Kim Haynes Interface and Clock Products High-Speed Serial Link Applications Texas Instruments, Inc. 214-567-2057 Telephone -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ted Tontis Sent: Wednesday, October 03, 2007 10:20 AM To: [log in to unmask] Subject: Re: [TN] Via plugging with LPI soldermask... Bill, I used to specify in my manufacturing notes 'vias must be plugged using LPI solder resist' I was told more then one once and from different suppliers that they could not guarantee the vias would be 100% 'plugged' using LPI. They would however guarantee that there would be LPI in the via hole or that the LPI would tent over the via, leaving a void in the center. If I required 100% via fill I would have to require that they fill the holes with some type of conductive filler. Thank you, Ted T -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brooks,Bill Sent: Tuesday, October 02, 2007 3:44 PM To: [log in to unmask] Subject: [TN] Via plugging with LPI soldermask... Just a quick question... When specifying 'plugged' vias using LPI soldermask... what is the actual process used to accomplish this procedure? How do you make sure the vias are plugged and what is the proper acceptance criteria used to verify and inspect the finished results? What is an acceptable plugged via vs. a reject? Is there a spec or standard that spells this out process and inspection criteria and method for reference? Thanks in advance... Bill --------------------------------------------------- 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 ----------------------------------------------------- ________________________________________________________________________ Email and AIM finally together. You've gotta check out free AOL Mail! - http://mail.aol.com --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------