Hi, Steve.
What you state is absolutely true. And it may not be from the paste manufacturer themselves, but from the distributor's handling practices, or lack thereof.
One should always use a certified distributor, so if a bad lot is discovered the paste vendor can contact you through the certified distributor. A certified distributor also is audited by the better paste companies to make sure the storage and stock rotation practices are being done.
I once had a buyer who would purchase solder paste from both the certified distributor, and the same paste from a different distributor who purchased the paste online. When we got a bad lot, the certified distributor notified me immediately and took back the bad lot. The buyer was told to re-purchase more on a no-cost p.o. to replace it. He placed the p.o. with the wrong distributor, the non-certified one. We received more of the bad lot! This is because only the certified distributor will be notified, not others, even if they are buying in large volumes.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephengregory5849
Sent: Saturday, August 16, 2008 10:46 AM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Exactly.
The vendor has earned my respect and appreciation for being so forthright.
They let me know as soon as they verified something was wrong so that I wouldn't spend any more time tweeking and and re-plotting my profile, which as we all know, when you're trying to assemble product to meet a schedule, can consume a fair amount of time.
My last order of paste is being completely replaced (as it should be). I think that both us, have learned something from this. We're both taking steps to prevent this from happening in the future.
The intent of my original post was not to bash a particular solder paste vendor. It was to give a visual to a problem that if you see something like this, and you're fairly confident that your profile is in the ballpark (like I was), then suspect the paste.
I've been involved in SMT since I got out of the Navy in 1987, and have worked for many different companies. At each company I've had the opportunity to be exposed to different paste vendors (Kester, Alpha, Indium, Amtech, Aim, Multicore, Senju, etc.), some were more widely used than others. One thing I can say from my experience, is that sooner or later, you'll get a bad lot of paste.
Steve
----- Original Message -----
From: "Mike Fenner" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 15, 2008 6:59 PM
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding , Etc,)
Didn't say it was profile, said it could be. If your vendor says it is powder and verified in their lab, then you have to at least give credit for being up front about it.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, August 15, 2008 6:37 PM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Hi Mike,
If it was the profile, why would the solder paste vendor tell me that the paste was bad and that they saw the same thing when they tested it in their lab?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Friday, August 15, 2008 11:27 AM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Well I think it looks like what we would call it "graping" - incomplete coalescence. A cause is powder oxidation, but it doesn't have to be as supplied. Could be the solder is oxidizing on reflow through flux exhaustion. So the fix is profile or a better flux activator.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, August 15, 2008 1:07 PM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Mornin' Inge and Everybody!
I have Inge's bony fish hanging on the wall at:
http://stevezeva.homestead.com/files/troubleshootingfishbone.jpg
I have no experience at all with wire bonding, but after looking at the diagram, I have a question; is one of the bones under "visual inspect" from a Tiger Woods fishbone? Hmmmm...
I heard a new term yesterday. It's called "snotballs". We were building an assembly using SAC305 paste on a ENIG finished PCB. Loaded up a profile that after plotting, was within all time and temperature parameters that the solderpaste vendor recommends. After reflow the joints looked like this:
http://stevezeva.homestead.com/files/Snotballs.jpg
Of course we were very surprised at the appearance, solderballs all over the surface of the fillets. We couldn't figure out what was wrong. After cleaning, all the balls went away and the joints looked fine. A phone call was made to our paste vendor, and they asked for the lot number of our paste.
Some tests were done from the lot of paste that was shipped to us and it was determined to be a bad lot of paste, we're getting new paste tommorrow. They told us that the appearance was something they called; "snotballs", and was probably due to badly oxidized powder. There wasn't a reason given of how this happened. The paste was made last month. I'm just sharing this image so that if you see something like this, it will give a clue that the paste is probably bad.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, August 15, 2008 3:05 AM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Arnoud et netters,
I've finally found the troubleshooting fishbone for wirebonding. I will ask Dr Gregory about presenting it on the Zevawall. Don't feel miserable when you see it...wire bonding use to work without any of the fishbone problems.
Keep the bone, care not to loose it, worthful for production people.
Inge
-----Original Message-----
From: Hernefjord Ingemar
Sent: den 13 augusti 2008 13:12
To: 'TechNet E-Mail Forum'
Subject: RE: [TN] NiAu Specification for Al Wedge Wire Bonding
This is not a fishbone, but you can make a bone of it, if you fish...wish
Wire bonding trouble shooting list:
1. Wrong loop height
2. Improper wire diameter
3. Wire elongation not adapted to object.
4. Wire alloy (doping)
5. Wire age (some wires have limited shelf life) 6. Bonding tool radius 7.
Bonding tool face polish type 8. Bonding tool, build-up of debris in chamfer and on face 9. Tool vibration amplitude and/or frequency inadequate 10.Bond force not adequate 11.Bond time not adequate, frequency swing not correct 12.Microscopic damage on wire caused by burrs in the tool 13.Intermetallic growth between wire and pad metallisation
(about 10 compounds known, some of which very brittle) 14.Impurities on or in the bond pads, either they are thickfilm or PWB 15.Inadequate metallisation thickness vs. dielectric thickness 16.The ultrasonic energy causes delamination of bond pad metallisation 17.The wire vibrates too much in the tool, wire gets microcracks and heel damage 18.The deformation of the wedge/ball is not sufficient, or is overdone.
19.Insufficient number of microwelds
20.Outgassing of polymers or other stuff, which can cause bond lift or bad bond yield 21.The bond pad micro structure (asperity)is too rough 22.Diffusion of metals or other stuff, which can change the characteristic.
23.Kirkendall voids, which makes bonds brittle and weak.
24.Maximum current exceeded in bond wire, can cause electro migration 25.Thermal moves that causes bond weakening through defects in the crystalografic structure 26.Hydrogen bubbles in the metallisation.
27.Presence of halogens in the ambient atmosphere can reduce bond yield 28.Cratering in semiconductor bond pads, too far gone and the wire bond will lift.
29.Fluorocarbons, chlorides or other residues from the semiconductor process will disturb the bond process 30.The ultrasonic energy is not correctly 'grounded'(insufficient clamping)
Especially important for large boards 31.Some wires or PWBs or substrates should be stored in dry nitrogen
until the day of wire bonding.
32.So called 'lubricants' may inhibit bond success, e.g. finger prints 33.Contaminations, from the machinery in automatic lines, can contaminate.
34.The superficial surface of Thickfilm gold or silver/palladium pads contain too much of Si, Bi, or Cd 35.Corroded metallisation of bond pads.
36.Oxides on bond pads
37.Microscopic amounts of water (temporarily), from inadequate storage 38.Microscopic amounts of water from humid ambient
The list is from one of my technical reports, there may be something missing...
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: den 11 augusti 2008 14:05
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Arnaud et TNetters,
I've not found the wirebonding fishbone, it's so tiny that my cats may have eaten it all. How ever however, another fishbone may serve some of you, I'll send it to Dr Gregory , and well packaged so that the custom people don't feel the smell.
Ineg
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of arnaud grivon
Sent: den 15 mars 2007 14:51
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding
Thanks for the cake, but coming back to the initial question, is there any standardisation or good practices for the NiAu plating used for Al wedge bonding?
Best regards,
A. Grivon
Hernefjord Ingemar a écrit :
> Arnoud,
>
> There is a lot to say, I send a good cake to start with ( 4Meg offline).
> If any further questions, send smoke signal. Trikeman is guru.
> Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of arnaud grivon
> Sent: den 14 mars 2007 16:01
> To: [log in to unmask]
> Subject: [TN] NiAu Specification for Al Wedge Wire Bonding
>
> Hello TechNet,
>
> A question for wire bonding gurus (and I know there are some).
> What are the NiAu specifications adapted for Al wedge wire bonding?
> Ni & Au thicknesses, electrolytic or electroless, roughness,
> hardness....
> Are there some normalized documents covering these aspects (IPC,
> MIL...)?
> Thanks in advance.
>
> Best regards,
>
> A. Grivon
>
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