Wayne, others - The object of the photos was to illustrate delamination of mold compound from the surface of the device - which is what Chris was asking about in the beginning, I thought... Valid points have been made, but the object was not looking for a ball bonds to fail, none of the die were sheared off, these were test parts subjected to grueling test regimes [exception was the axial], safety bonds were there by design - not because of any bondability problems, colors may be off due to camera, lighting, etc., for confidentiality reasons I only illustrated a portion of the total assembly. The purpose was to provide Chris with a representative photo of what it looks like to have mold compound delaminate from the surface of the die [and yes, the mold compound can easily shear the die off]. Yes, the wire had to stretch along its length to ultimately fail as is did. Oh yes, these had some very unusual wire looping and EXTREMELY long wire spans for LEDs. Remedies include alternate molding parameters, optimized post-mold cure parameters, alternate materials, de-coupling materials, platings, mechanical anchor features, etc. etc... The blue color is a dye - I find that a blue Sharpie magic marker works very nicely. For some reason, the blue flowed better than Black or Red. The Sharpie ultra fine tip does not work as well as the larger tip. Regarding the axial LED delamination. After they cleaned up the process, it was much better. Enjoy Steve Creswick http://www.linkedin.com/in/stevencreswick -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW Sent: Monday, June 14, 2010 12:51 PM To: [log in to unmask] Subject: Re: [TN] LED wiring bonding The pix make it seem like you are looking for the ball bond weld to fail. That should be impossible. Some of your pix look like there may be a smeared-over crack/cleavage at the wire in the heat affected zone. That can absolutely happen: Molding material moves, causes wire to shear, molding material moves back to original position, shear closes up, and you get continuity if you're lucky. Then cross sectioning smears the gold across the gap, and you're left scratching your head! Wayne Thayer -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna Sent: Monday, June 14, 2010 11:33 AM To: [log in to unmask] Subject: Re: [TN] LED wiring bonding Just uploaded some of pictures from the project that started this thread. Kevin, I think your warning from Nichia applies to this job. I have not seen such warnings from the manufacturer of these. http://ipc-technet.groupsite.com/galleries Ir Emitters Chris Au. No necking or breaking was noted. We believe that there may be some correlation to the increased CTE of "optically clear" encapsulation vs. not so clear or tinted. But the underwriting of my project is gone, for now. Chris From: Werner Engelmaier [mailto:[log in to unmask]] Sent: Thursday, June 10, 2010 2:34 PM To: [log in to unmask]; Chris Mahanna Subject: Re: [TN] LED wiring bonding Hi, Are we sure it is the bond and not the wire itself that is breaking? We eed to know whether we are dealing with Au or AlSi wire. Been working on a wire break case. Werner -----Original Message----- From: Chris Mahanna <[log in to unmask]> To: [log in to unmask] Sent: Thu, Jun 10, 2010 1:13 pm Subject: Re: [TN] LED wiring bonding I forwarded some optical pictures to Steve. Steve, you're welcome to post them. Chris -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez Sent: Thursday, June 10, 2010 8:04 AM To: [log in to unmask] Subject: Re: [TN] LED wiring bonding Fellow TechNetters: Was anyone able to provide a photo(s) of this LED bonding issue. Victor, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick Sent: Tuesday, May 11, 2010 5:32 AM To: [log in to unmask] Subject: Re: [TN] LED wiring bonding Chris, I get the shivers when people say they have a bond lift, because my instinct tells me the process was not where it should have been, but there is still room for optimism. If properly bonded, and subsequently torn or sheared apart, I expect to see a good deal of viable intermetallic beneath the bond. If there is little sign of intermetallic formation, there was little bonding taking place - read as not a very good bond in the first place. By analogy, if one is crafting with wood and gluing panels together with a good glue, then subsequently breaks the panel - the break should occur somewhere other than at the glue line. The glue should be stronger than the wood. As it is with wire bonding. The bond should be stronger than the wire itself. Regarding the blue dye. Not sure of the specific mold compound being used [you could at least ask to see the data sheet ...], but it has been my experience that the amount of dye used is actually extremely little. I doubt that it would have significant effect on CTE, but you could be on to something. Normally one tosses in a bunch of fumed silica, etc to help control CTE. This doesn't do too well for maintaining light transmission, however. I would also check to see if the clear and blue were actually cured the same way, etc. That may have more effect on the result than the pigmentation alone. If you have intermittent bonds due to delamination, etc. sometimes you can simply press on the device and get it to work again. You might also try a bit of gentle heat/cold - say refrig to room, etc. Am not a fan of the freeze spray stuff. Wire necking will come about after many temp cycles - aka hundreds depending on temp limits. It had better not occur after 1-4 reflow cycles! I may also have a pic of delam if Vlad can not locate his. Best wishes, Steve Creswick http://www.linkedin.com/in/stevencreswick -----Original Message----- From: Chris Mahanna [mailto:[log in to unmask]] Sent: Monday, May 10, 2010 10:33 PM To: TechNet E-Mail Forum; Steven Creswick Subject: RE: [TN] LED wiring bonding Steve, Awesome. Now that you've walked me through it, I think our customer has a mixed bag- some bond lifts and delam, all damaged by excessive soldering excursions. I guess maybe part of my question was whether delam was a latent defect from poor bonding.? Haven't found significantly necked down Au wires yet. Do you think they can get significantly better CTE, Tg out of blue lenses? On our job, the blue had half the failure rate of the clear, even though they are rated the same for soldering. BTW they are both really Ir emitters; clear lenses with the better spectrum. Thanks for the help. I will certainly try to get permission to post the pictures. I'd like to see Vladimir's SEM image. Is there further FA to be gleaned from SEM? Thanks Werner! Wayne, yes I believe that was the official blame game from the component manufacturer. What do they look like when you burn them up? I'd expect to see burnt plastic too.?? Chris -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick Sent: Monday, May 10, 2010 6:49 PM To: [log in to unmask] Subject: Re: [TN] LED wiring bonding Chris, Ahh! Something I can help out with. A great deal depends on the package structure, obviously wire bonding process control, and whether it is Au or Al wire. Wire bonding defects are rare, if the materials and process is under control. The caveat is that Pb-free reflow temps may cause extra expansion in the molding compound as the material goes above it Tg during reflow/s. Many/most clear mold compounds have Tg's in the <135-155°C range. Can't put silica in there to help modify the CTE... Moving mold compound during temp cycles can often break the bond wire near mid-span. The wire will actually neck down to the shape of an hour-glass funnel as it stretches. ... then breaks. Oops. You can also get bond lifts, but if that is the case you may also see delamination from the bonding surface. Hard to describe what it looks like other than to say that you can see an air-gap there.. If you don't see the delam, one just may have a poor bond. You can also shear the ball/bond off the die, but many times one will place a low modulus material on top of the chip to mechanically de-couple from the higher modulus molding compound in an attempt to alleviate this. First thing to do is x-ray to find where the discontinuity is. If that fails, then move on to selectively polishing the device down so that you can see inside clearly. I have been known to take a really tiny 0.010-0.015" dia drill bit in a pin vise to gain access to the interior for dye testing to check for delamination [but that can be classified as destructive - although certainly illustrative!] Lastly, it may also be possible to shear the die off, but like you, I would look at the wire first. A quick look at the bonds can often tell you if they are over bonded, or something was moving during bonding. Once you get it polished flat, you may be able to get a reasonable picture. Steve Creswick http://www.linkedin.com/in/stevencreswick -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna Sent: Monday, May 10, 2010 5:49 PM To: [log in to unmask] Subject: [TN] LED wiring bonding It's all LEDs these days! We have an FA that shows poor wire bonds to GaAlAs/GaAs in microsection after assembly. The failure is seen in the parts per hundred across different lots and slightly different part numbers of LEDs. The assumption would be that LED wiring bonding defects are very rare. Is there something particular about these? Or is it the crimping and/or Pb-free assembly that is pulling them apart? The ones that seem more susceptible are GaAlAs Double Heteros. Thanks. Chris ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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