Dennis (and Brad), I may have opened Pandora's box. In essence I was trying to state that new technologies are dictating changes in procedures. Some of them are driven by cost, some by size, some of them by governments. Some issues of reliability are of great concern, especially with lead-free. This issue alone could be addressed with reams of paper and days of seminars and still wouldn't be completely covered.
Regarding vias and hole sizes, that is another topic that can take a lot of time to completely address. My suggestion is that if you have something that works now, don't change it. If you don't have to resort to vias in pads or microvias, don't do it. I regret that in my haste I neglected some pertinent issues that really can't be addressed in an email....such as amount of copper content, should you use solder mask and where, stencil thickness, and in the case of BGA, whether you use paste or just flux. So let me back up and say that IPC is a good resource of information and instruction. This is what we know works. If different techniques are dictated, then you may have to determine how reliable the end result is until IPC or others complete the work. I really don't want to belabor the point, but for years we have been told not to use a tin finish because of whisker growth. Now some lead-free boards and components are tin plated and solder has a high tin content. We know this isn't the best approach, but it is being done. The same holds true for fluxes and chemical cleaning. No-clean flux has it's issues, but sometimes you have to use second best. One of the reasons Brad is upset with all of this is reliability. If somebody's life depends on the working of your product you don't want to be experimenting with questionable methods. Then again, it may be perfectly ok to use alternative methods with a cheap throw away consumer item. And the DAP is Data Acquisition Products...primarily A/D and D/A converters. Bob Benjamin DAP - Texas Instruments Tucson, AZ (520) 746-7753 -----Original Message----- From: Dennis Saputelli [mailto:[EMAIL PROTECTED] Sent: Thursday, December 08, 2005 6:49 PM To: Protel EDA Discussion List Cc: Bob Benjamin Subject: Re: [PEDA] Via size, lead free, etc. thanks for your most helpful comments Bob but the 13 mil hole via in pad certainly is a surprise to me is that a finished size after plating or the drill size ? i certainly understand the relation to the pad size and minimum annular ring reqs getting rid of the dog bones without resorting to laser drilling would be a major boon heck it would be great to put them in bypass cap pads for that matter, you would get better performance and more routing room bob, how was your 6 mil (i assume finished size) hole fabricated, laser or mechanical drill? and the cleaning question re QFN and BGA still interests me, whether lead free or not it seems to me that using the good old OA water soluble flux this is too risky to use due to the difficulty of cleaning under these things so is 'no clean' flux the typical method ? does anybody still use RMA for this sort of work? BTW, Bob, what is 'DAP' ? Dennis Saputelli _______________________________________________________________________ Integrated Controls, Inc. Tel: 415-647-0480 EXT 107 2851 21st Street Fax: 415-647-3003 San Francisco, CA 94110 www.integratedcontrolsinc.com Bob Benjamin wrote: > All, > > > > I get the digest version, so I'm responding after reading a number of > messages regarding via sizes. The answer to Brad's original question is > yes, via in pad is the recommended connection for fine pitched BGA. Believe > it or not, the via size is going to be dictated by the pad size more than > by the solder thieving problem. The last one I did had a 6mil hole. We > have used 13 mil holes as the largest, and that is the info we have been > putting into app notes for our devices. > > > > You will also see this with QFN devices that have the large pad used to > stabilize the package, as well as adding thermal relief. This tiny pad on > devices, such as op amps, can be tied through vias to ground planes to draw > off heat from the device. This is one of the places I have used the 13 mil > holes. > > > > So is it recommended?..yes,..and does it work?....yes. If it really bothers > you, plug the holes with silver or epoxy. > > > And by the way, there is lead-free BGA that works well with no-clean > flux..or so I'm told by Kester. Dell, Nokia and Motorola are using LF > processes, and many of the parts they are using are BGA. One thing to > consider is LF parts are going to be the norm in the not too distant future. > There may be problems procuring leaded parts so keep this in mind. > > > If you would like to discuss this further, I am willing to do this, just > contact me directly. > > > Bob Benjamin > DAP - Texas Instruments > > Tucson, AZ > > [EMAIL PROTECTED] > ____________________________________________________________ You are subscribed to the PEDA discussion forum To Post messages: mailto:[email protected] Unsubscribe and Other Options: http://techservinc.com/mailman/listinfo/peda_techservinc.com Browse or Search Old Archives (2001-2004): http://www.mail-archive.com/[email protected] Browse or Search Current Archives (2004-Current): http://www.mail-archive.com/[email protected]
