At 11:09 AM 2/5/2002 +1100, you wrote: >Yes, but the power connections are made through the Vias are they not? >There are over 100 ground and 3.3V/2.5V balls that connect to internal >planes through Vias. At least for this particular BGA. Therefore, wouldn't >the thermal effects still be relevant in this case?
Actually, a related question I had that seems to tie in to this one... I have been told by some engineers that they often like to put a 'via per pad' when working with BGAs, especially when doing prototypes. Part of the reason for this being you have all of the connection-points on the BGA part available as testpoints and/or solderpoints on the opposite side of the board for those lovely last-minute fixes on prototypes. (Also, several companies make direct BGA<->PGA snap-in adapters for prototyping that keep the EXACT BGA footprint extended into PGA, making it possible (from what I have been told by a sales rep) to open up your vias and simply drop their adapter in as a fine-pitch PGA thru-hole device. When it comes time to do a production run, you simply shrink the diameter of the vias and attach your BGA devices normally.) I can obviously see that putting vias into the pads directly could potentially cause 'robbing' to occur if too large of a diameter was used, as well as the 'thermal stressing' due to cooling from power planes. (Colin mentioned 'plugging' vias under the BGA - is there a way to do this without using blind/buried? I'm unfamiliar with the term...) I have also been told by an assembly technician that a lot of times they prefer all BGA pads to have a via in them for thermal conduction from the other side, as it can potentially help the reflow process. My question (for the BGA masters out there!) that may help to partially answer the question about thermal relief for the vias... Do you typically place your vias directly IN the pads, or do you create an array of vias offset from the actual landing pads? (I've seen the 'offset via' approach documented by several companies in various appnotes) In the direct via-in-pad approach I can see the need for the thermal-separation as was mentioned... But in the offset-grid approach, I suppose it wouldn't matter, since not much heat will theoretically get conducted across the trace from BGA pad to via to make an appreciable difference. Any comments about this from those who have worked with BGA? Trying to get all of the facts, since some upcoming designs we are planning on working on need to be based on parts only available in BGA. :/ (P.S. THANK YOU again to all of the folks that replied to my question last week concerning autorouting vs manual routing! You all are an absolute goldmine of technical knowledge. Thanks for sharing!) -- Matt >At 06:10 PM 4/02/2002 -0500, you wrote: >>At 08:34 AM 2/5/2002 +1100, Colin Weber wrote: >> >>>I was talking with another designer, Phil Dutton, and he aslo >>>recommended the Power Connections Relieved. >>>"Make sure that your Power connections are relieved, or they will cool >>>down faster than the rest of the device, inducing stresses." >> >>That is "Power Connections." We've been talking about vias. Different animal. >> >>[EMAIL PROTECTED] >>Abdulrahman Lomax >>Easthampton, Massachusetts USA > > >Regards, > >Colin Weber * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:[EMAIL PROTECTED] * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:[EMAIL PROTECTED] * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://firstname.lastname@example.org * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *