I once consulted on problem like you describe. The company was using through hole LEDs for signs. The board design had been unsupported single side. An EMS suggested that it would be better for them to provide PTH to better support the leads. Shortly after they started using the PTH version of the board they began to see LED failures. A lot of FA was done. The actual failure was internal to the LED. A wire bond was being pulled inside the LED package. I don't recall if it was the Cathode or Anode side. Not all but some were intermittent. We never identified the mechanism by which the damage was done but returning to an unsupported design, one that prevented solder from touching the package, eliminated the LED failures. We did some tests with the LED in a PTH with a standoff. They did not fail. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea Sent: Tuesday, June 03, 2008 7:55 AM To: [log in to unmask] Subject: [TN] Intermitent contact on LEDs Dear Technos, I am investigating some returns from the field and can't really figure out what the problem is. On boards having 200+ TH LEDs we see 4 to 10 malfunctioning ones, but if pressure is applied on the component it starts functioning. Under my regular microscope I cannot see any problem with the joints and when removed, the LEDs work properly. One unpleasant thing though is that the LEDs were machine inserted and clinched to the board pretty tightly, so the solder did not wick up on the leads too much, but if the joint was somehow fractured, applying pressure on the component would only widen the gap, since the bulk of the joint is on the opposite side of the pressure point, am I right? The PCB is a regular 0.062" thick 2 layer board, with the regular 1oz of Cu on each layer, of pretty impressive dimensions, 22"x10". There is no pattern in the disposition of the malfunctioning LEDs. Besides cracked PTH, which we will investigate since I am preparing to send out some boards for cross-sectioning, can it be anything else? Thanks, Ioan --------------------------------------------------- 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 -----------------------------------------------------