I guess that's a good question for Motorola. We (designers) have used a "rule of thumb" that says the land size should be no larger than 1/2 of the ball pitch. Diameter .4mm fits that rule. I cannot testify as to whether or not it's a good rule... I'm just parroting what I've been told. We also TEND to follow the manufacturer's recommendations (when they are given). -Denis At 12:42 PM 11/19/2001 -0500, you wrote: >The rule of thumb, as I understand it, is 80% of the smallest ball size or >preferably the same size as the substrate land. The object being to control >the collapse of the solderball. > >If the minimum ball size is 0.35mm, how can you (or Mortorola) justify a >pad size of 0.4-0.5mm? > >At 10:40 AM 11/19/01 -0600, you wrote: >>Date: Mon, 19 Nov 2001 07:42:59 -0800 >>From: Denis Lefebvre <[log in to unmask]> >>Subject: Re: TechNet Digest - 18 Nov 2001 to 19 Nov 2001 - Special issue >> (#2001-713) >> >>As a layout designer, I am surprised that they used such small land areas. >>Motorola recommends a land of .40 to .50mm. IMO .28mm is insufficient. >>See attached PDF from Motorola. >> >>Denis Lefebvre, C.I.D. >>Senior PCB Designer >>Finisar Corporation >>(408)542-3832 >>http://www.finisar.com >> >>At 10:16 AM 11/19/2001 -0500, you wrote: >> >I'm not that far up in the food chain to know all of the particulars, but >> >it wouldn't surprise me if that were the case. >> > >> >What I'm looking for is comments on the increase of pad size and >> >corroboration in my belief that it's the wrong solution to this problem. >> > >> >Tom >> > >> >At 04:20 AM 11/19/01 -0600, you wrote: >> >>Date: Mon, 19 Nov 2001 08:20:31 -0000 >> >>From: Eric Dawson <[log in to unmask]> >> >>Subject: Re: BGA bone of contention >> >> >> >>Hi Tom, >> >>Are you wave soldering the other side of the board with the reflow >> soldered >> >>bga.s on top? I have come across this practice and it definitely disturbs >> >>the bga joints causing opens which cannot be detected by ordinary X ray >> >>inspection. >> >>Hope this helps. >> >>Regards >> >>Eric Dawson >> >> >> >> > -----Original Message----- >> >> > From: Tom Colby [SMTP:[log in to unmask]] >> >> > Sent: Friday, November 16, 2001 8:47 PM >> >> > To: [log in to unmask] >> >> > Subject: [TN] BGA bone of contention >> >> > >> >> > Help me out with this technetters, >> >> > >> >> > The problem: BGA opens on a HASL board. >> >> > >> >> > The device: Motorola MCF5272, a 196 MAPBGA, 1mm pitch, ball size of >> >> > 0.35/0.65. Substrate land size unknown. Footprint designed with a >>pad of >> >> > 0.28mm. >> >> > >> >> > Management's solution is to increase the pad size to 0.4mm. I say to >>look >> >> > elsewhere in the process for the problem. >> >> > >> >> > I'd like to hear the opinions of my esteemed colleagues. What do >> you say >> >> > folks? >> >> > >> >> > Thanks in advance, >> >> > >> >> > Tom >> >> > >> >> > >>-------------------------------------------------------------------------- > >--------------------------------------------------------------------------------- >Technet Mail List provided as a free service by IPC using LISTSERV 1.8d >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 delivery of Technet send the following message: SET >Technet NOMAIL >Search previous postings at: www.ipc.org > On-Line Resources & Databases > >E-mail Archives >Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional >information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 >ext.5315 >--------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------