So, when these venerable suppliers fall outside of the range of their process capabilities, what benchmarks are used to determine what went wrong, if no standards are required?
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, January 06, 2010 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
You learn to trust your supply. It is such a specialized area you do not want to risk lost your reputation. The vendor has more skin in the game than you can imaging. That is how they are the few still standing. The problem for most of the assemly house in US, you do not have large enough volume even get their attention. Check taiwan and singapore contract mfg house, see who is their supply will tell you the story. Too bad, US has fall off the radar screen on the wire bondable gold supply for now.
--------------------------
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Wed Jan 06 09:59:30 2010
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
Joyce,
And if they do a Weibull plot on their data, you can see changes in the
characteristic strength, etc. from lot to lot and use that as a
accept/reject gauge before it even leaves their house. The platers/shops I
like to work with have bonders. However, sometimes you have to train them
how to use them.... :-( Anyone can smash the bejeebers out of a 'bond' and
call it 'good'. That is not the way I prefer to play the game! I can also
play with looping to fudge the numbers too. Have to keep your eyes open -
'trust' but verify!
Been there done that!
Regarding thin Nickel [<50 µinch] there is one situation where you can
usually get away with it - Aluminum wire with absolutely no prior thermal
excursions to the part.
If you subject the part to a reflow operation and it has thin and/or porous
nickel, you will experience increased bonding difficulties as compared to a
virgin board without the thermal excursion. Shows up on Weibull plots too!
As time after thermal exposure increases, even more of the diffused copper
will oxidize, further increasing bonding problems.
I don't believe the rate of Cu diffusion thought the Ni is all that great at
room temp. It is my opinion based on bonding parts over the years that you
need that thermal kick to get it moving. Once the copper gets up into the
gold, bondability goes down the toilet very quickly! You can even see the
color change by eye in many cases. Maybe Dave H has an equation for the
diffusion rate, or desires to chime in.
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Wednesday, January 06, 2010 9:43 AM
To: [log in to unmask]
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
It all boil down to volume vs price. If you have volume and price
advantage, you will find the top supply house (at least one or two, if not
three). No standard required. It is such a highly specialized area that in
house spec is good enough. The guys make the high end large volume even has
wire bonder in QA with the bond pull force listed for every batch (if you
pay top dollar).
--------------------------
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Wed Jan 06 09:17:55 2010
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
This begs the question, are there IPC or other standards for die and wire
bonding that define what the specific alloys and nickel thickness and the
gold thickness ranges shall be, similar to those within IPC 4552 and 4553?
Looking back at these issues in doing a search of the forum archives, it
appears that this is an issue that many people keep struggling with.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of [log in to unmask]
Sent: Wednesday, January 06, 2010 8:14 AM
To: [log in to unmask]
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
Hi Steve,
Nickel below 80-90 microinches will not act as a barrier due to porosity.
You may get copper migration at 40 microinches of Ni which will effect
bonding.
Regards
Aleks Lozinsky
Technical Sales Representative
Technic Canada Inc.
Office: 905-940-4020
Cell: 416-450-1093
E-mail: [log in to unmask]
-----Original Message-----
From: Steve Kelly <[log in to unmask]>
Date: Wed, 6 Jan 2010 08:50:49
To: <[log in to unmask]>
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
Hi Steve et al,
Unfortunately this is not as easy as it sounds. First the lower pull
strengths are not necessarily a failure- they are just not as good. This was
an experiment designed between ourselves and our customer. The initial
problem is we have a .0032 wide flying lead ( about 150 of them) with no
kapton support. A chip/die is "compression bonded" onto the lead - from what
I can gather it is a combination of heat/pressure/ultrasonic and some kind
of proprietary magic. The reason we went to the lower nickel is because the
leads being so fragile they often crack during the process so we tried the
lower nickel to alleviate this issue. With the lower nickel pull is approx.
5-7 grams. With the higher nickel 9-11 grams. There is a gold bump on the
die and when the failure happens the gold bump separates from the lead with
no damage to the gold bump. At present this is as much as I know. Thanks for
the input so far. Steve Kelly
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: January-05-10 6:14 PM
To: [log in to unmask]
Subject: Re: [TN] Pull strength of thermosonic wire bondable gold
Steve,
If you can send me the data sets in an Excel format, I can provide you with
some insight based on magnitude and grouping by Weibull plot.
If there is a big mix of failure modes, this interpretation will be pretty
generic.
Its free input, however :-)
Just send it direct.
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Tuesday, January 05, 2010 4:17 PM
To: [log in to unmask]
Subject: [TN] Pull strength of thermosonic wire bondable gold
Hi All,
I have a wire bond question to the wire bond gurus who have helped me out a
lot in the past. Made 2 versions of a flex circuit - only varied the nickel
thickness. Application is thermosonic gold wire bonding.
Flex circuit lead is .0032 wide - version 1 - nickel is 150 microinches -
soft gold is 50 microinches- pull strength is X
Version 2 - nickel
is 40 microinches - soft gold is 50 microinches - pull strength is approx.
˝X of version 1-
Is this what I should expect?
Regards Steve Kelly
Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)
(416) 750-8433 (work)
(416) 750-0016 (fax)
(416) 577-8433 (cell)
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