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June 2010

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Date:
Thu, 10 Jun 2010 23:30:59 +0200
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Has Steve pasted the photos? Seen nothing at the moment. Am curious, have 
inspected hundred thousands wire bonds (that's the disadvantage of being 
expert on something)

Inge

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From: "Chris Mahanna" <[log in to unmask]>
Sent: den 10 June 2010 20:56
To: <[log in to unmask]>
Subject: Re: [TN] LED wiring bonding

> 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.
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> Steve, you're welcome to post them.
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> Chris
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> -----Original Message-----
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> From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf 
> Of Victor Hernandez
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> Sent: Thursday, June 10, 2010 8:04 AM
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> To: [log in to unmask]<mailto:[log in to unmask]>
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> Subject: Re: [TN] LED wiring bonding
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> Fellow TechNetters:
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>   Was anyone able to provide a photo(s) of this LED bonding issue.
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> Victor,
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> -----Original Message-----
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> From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf 
> Of Steven Creswick
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> Sent: Tuesday, May 11, 2010 5:32 AM
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> To: [log in to unmask]<mailto:[log in to unmask]>
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> Subject: Re: [TN] LED wiring bonding
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> Chris,
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> I get the shivers when people say they have a bond lift, because my 
> instinct
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> tells me the process was not where it should have been, but there is still
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> room for optimism.
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> If properly bonded, and subsequently torn or sheared apart, I expect to 
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> a good deal of viable intermetallic beneath the bond.  If there is little
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> sign of intermetallic formation, there was little bonding taking place -
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> read as not a very good bond in the first place.
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> By analogy, if one is crafting with wood and gluing panels together with a
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> good glue, then subsequently breaks the panel - the break should occur
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> somewhere other than at the glue line.  The glue should be stronger than 
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> wood.  As it is with wire bonding.  The bond should be stronger than the
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> wire itself.
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> Regarding the blue dye.  Not sure of the specific mold compound being used
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> [you could at least ask to see the data sheet ...], but it has been my
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> experience that the amount of dye used is actually extremely little.  I
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> doubt that it would have significant effect on CTE, but you could be on to
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> something.  Normally one tosses in a bunch of fumed silica, etc to help
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> control CTE.  This doesn't do too well for maintaining light transmission,
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> however.  I would also check to see if the clear and blue were actually
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> cured the same way, etc.  That may have more effect on the result than the
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> pigmentation alone.
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> If you have intermittent bonds due to delamination, etc.  sometimes you 
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> simply press on the device and get it to work again.  You might also try a
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> bit of gentle heat/cold - say refrig to room, etc.  Am not a fan of the
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> freeze spray stuff.
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> Wire necking will come about after many temp cycles - aka hundreds 
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> on temp limits.  It had better not occur after 1-4 reflow cycles!
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> I may also have a pic of delam if Vlad can not locate his.
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> Best wishes,
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> Steve Creswick
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> http://www.linkedin.com/in/stevencreswick
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> -----Original Message-----
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> From: Chris Mahanna 
> [mailto:[log in to unmask]<mailto:[log in to unmask]>]
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> Sent: Monday, May 10, 2010 10:33 PM
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> To: TechNet E-Mail Forum; Steven Creswick
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> Subject: RE: [TN] LED wiring bonding
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> Steve,
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> Awesome.  Now that you've walked me through it, I think our customer has a
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> mixed bag- some bond lifts and delam, all damaged by excessive soldering
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> excursions.  I guess maybe part of my question was whether delam was a
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> latent defect from poor bonding.?  Haven't found significantly necked down
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> Au wires yet.
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> Do you think they can get significantly better CTE, Tg out of blue lenses?
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> On our job, the blue had half the failure rate of the clear, even though
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> they are rated the same for soldering.  BTW they are both really Ir
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> emitters; clear lenses with the better spectrum.
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> Thanks for the help.  I will certainly try to get permission to post the
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> pictures.  I'd like to see Vladimir's SEM image.  Is there further FA to 
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> gleaned from SEM?
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> Thanks Werner!
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> Wayne, yes I believe that was the official blame game from the component
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> manufacturer.  What do they look like when you burn them up?  I'd expect 
> to
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> see burnt plastic too.??
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> Chris
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> -----Original Message-----
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> From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf 
> Of Steven Creswick
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> Sent: Monday, May 10, 2010 6:49 PM
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> To: [log in to unmask]<mailto:[log in to unmask]>
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> Subject: Re: [TN] LED wiring bonding
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> Chris,
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> Ahh!  Something I can help out with.
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> A great deal depends on the package structure, obviously wire bonding
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> process control, and whether it is Au or Al wire.
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> Wire bonding defects are rare, if the materials and process is under
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> control.
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> The caveat is that Pb-free reflow temps may cause extra expansion in the
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> molding compound as the material goes above it Tg during reflow/s.
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> Many/most clear mold compounds have Tg's in the <135-155°C range.  Can't 
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> silica in there to help modify the CTE...
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> Moving mold compound during temp cycles can often break the bond wire near
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> mid-span.  The wire will actually neck down to the shape of an hour-glass
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> funnel as it stretches. ... then breaks.  Oops.
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> You can also get bond lifts, but if that is the case you may also see
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> delamination from the bonding surface.  Hard to describe what it looks 
> like
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> other than to say that you can see an air-gap there..  If you don't see 
> the
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> delam, one just may have a poor bond.
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> You can also shear the ball/bond off the die, but many times one will 
> place
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> a low modulus material on top of the chip to mechanically de-couple from 
> the
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> higher modulus molding compound in an attempt to alleviate this.
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> First thing to do is x-ray to find where the discontinuity is.  If that
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> fails, then move on to selectively polishing the device down so that you 
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> see inside clearly.
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> I have been known to take a really tiny 0.010-0.015" dia drill bit in a 
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> vise to gain access to the interior for dye testing to check for
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> delamination [but that can be classified as destructive - although 
> certainly
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> illustrative!]
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> Lastly, it may also be possible to shear the die off, but like you, I 
> would
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> look at the wire first.  A quick look at the bonds can often tell you if
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> they are over bonded, or something was moving during bonding.  Once you 
> get
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> it polished flat, you may be able to get a reasonable picture.
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> Steve Creswick
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> http://www.linkedin.com/in/stevencreswick
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> -----Original Message-----
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> From: TechNet [mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf 
> Of Chris Mahanna
>
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> Sent: Monday, May 10, 2010 5:49 PM
>
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> To: [log in to unmask]<mailto:[log in to unmask]>
>
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> Subject: [TN] LED wiring bonding
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> It's all LEDs these days!
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> We have an FA that shows poor wire bonds to GaAlAs/GaAs in microsection
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> after assembly.  The failure is seen in the parts per hundred across
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> different lots and slightly different part numbers of LEDs.
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> The assumption would be that LED wiring bonding defects are very rare. 
> Is
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> there something particular about these?  Or is it the crimping and/or
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> Pb-free assembly that is pulling them apart?
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> The ones that seem more susceptible are GaAlAs  Double Heteros.
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> Thanks.
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> Chris
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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
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