They're all flipping in the same direction -- is this normal or another clue? -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Thursday, November 02, 2006 10:41 AM To: [log in to unmask] Subject: Re: [TN] Bizzare Phenomena... Mornin' Richard! I was busy yesterday installing a new (reconditioned) VCD, so that's why I haven't replied much about my problem. I agree with you about the small particles coalescing into larger ones, and I do think that both my tombstoning and oven solderball problem are definitely related. But I'm baffled why I'm having this problem. I've been trying to eliminate all the causes that we could possibly be introducing in order to solve this. I've had tombstones before, and I've always been able to find the root cause and take care of it, or at least understand why it may be happening, such as in a case on a board where the footprint of the two pads for 0805 passives were too far apart. In that case, the board was re-spun and the problem went away. These tombstones are really baffling me! I've even had some big ferrite inductors stand on their heads! Check out: http://stevezeva.homestead.com/files/0402_Tombstone.jpg http://stevezeva.homestead.com/files/0805_tombstone_2.jpg http://stevezeva.homestead.com/files/Ferrite_Tombstone.jpg Both boards have double sided SMT. The pictures you see are before wash, and you don't see any solderballs on the PCB to speak of. The paste print is dead-on, and we're not overprinting anything on the boards. The board with the 0402's has a 5-mil stencil, and the board with the ferrite beads and 0805's has a 6-mil stencil. Placement has been dead-on and we're using a Fuji Aim platform for placement. Our ovens are Heller 1809's and we're reflowing in air. Pad geometries on both assemblies look absolutely fine, nothing out of the ordinary at all. Below is one of the plots that I did on the board that has the 0402 tombstones: http://stevezeva.homestead.com/files/2246_Bottom_Wednesday.jpg I will say that I might be a little steep in the very beginning of the profile, but it's not overly steep...about 4-6 C. per second, but then smooths out during the remainder of the profile and slowly rises in a ramp-to-spike type of profile. I've got 1000-grams of a new batch of solderpaste from our vendor, and I'm waiting for another job to be able to try it. The one change I made with this new batch is that it is type-3 mesh instead of type-4. There is nothing on the board that requires a type-4 mesh. This has been one of the strangest and most frustrating issues that I've run across in a long time. I hope the paste change fixes it... -Steve Gregory- -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. Sent: Tuesday, October 31, 2006 10:49 AM To: [log in to unmask] Subject: Re: [TN] Bizzare Phenomena... Steve, Judging by the small size of most of the particles, and if I look very closely I can see that it appears many of the particles have agglomerated into larger particles, I would assume that these are all very small solder balls that are being spit off of the board. Because they are in the reflow chamber, they sit down in the oven in a molten state continuously and if other solder spatters happen to land on them they are absorbed into the larger solder balls. This is why it appears that there are large solder spatters, when in fact they are not, just accumulations of small spatters. Why is it happening? BTSOOM. My first guess is that at the higher temperatures there is some spattering occuring as the paste goes into reflow. This can be attributed to outgassing of paste solvents and/or moisture in the paste, but there are many other possible causes, including outgassing from the pwb, printed solder paste not entirely on the pads, and many other potential causes. Something is obviously causing the molten solder to spatter, and these are only a few things that come to mind. Your profile does climb from 190 C to 250 C in about 3 or 4 minutes, and this might be enough to cause this type of spattering if the flux volatiles are not burning off fast enough. At first I wondered if excess solder paste was smearing the bottomside of the pwb during the printing process and falling off at reflow, but what would cause it to fall off? So, it is probably paste spattering. Whether the cause is boiling off of paste solvents or extraneous moisture from some other source, I am 99% sure that it is related to the tombstoning issues you mention. Fixing this problem will probably fix the other. I guess I would try going with a slightly longer profile with a more linear ramp-up and see if it improves. You may also want to evaluate different solder pastes. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Tuesday, October 31, 2006 8:57 AM To: [log in to unmask] Subject: [TN] Bizzare Phenomena... Mornin' All! This morning I have seen something that I have never, ever have seen before. It's been a little slow the past week, so we decided to do our maintenance on our reflow ovens. After we opened the oven up, we found many, many solderballs laying on the bottom of the oven right around zone 7 - 8, right at the beginning of the spike zone. Check-out: http://stevezeva.homestead.com/files/Oven_Solderballs.jpg http://stevezeva.homestead.com/files/Oven_Solderballs_2.jpg http://stevezeva.homestead.com/files/Oven_Solderballs_3.jpg http://stevezeva.homestead.com/files/Oven_Solderballs_4.jpg We've been having tombstoning problems when we've run the two lead-free jobs that we have here. I've been working with the paste vendor sending my profiles and plots, but I haven't been able to solve the problem. The solderballs in the oven are lead-free solderballs. We are using a Heller 1809, and my profile set-points are: 120 140 160 180 190 200 230 240 250 120 140 160 180 190 200 230 240 250 Belt speed 26 in per min The paste is a SAC 305 with a water washable no-clean flux. I think my profile is pretty reasonable, and the last board we ran is pretty standard, .062" thick, with no bizzare copper planes. The board finish with both jobs has been ENIG. The last job I ran we were tombstoning 0805's, the one before that we were tombstoning 0402's. With both jobs we've had major tombstoning problems. I've slowed the beltspeed down, sped it up, ramped up slower, ramped up faster, changed this, changed that, but still haven't resolved my tombstoning. Of course, I'm the only one that's having this problem according to my paste vendor... I wouldn't have imagined that I would see the solderballs in the oven like we have... Have any of you ever seen something like this before? -Steve Gregory- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 1.8e 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 1.8e 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 1.8e 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 -----------------------------------------------------