bond wire length

[zappedagain]

I've been told the maximum length to run a 0.001" Au bond wire is 0.065". Is this a standard telecom spec and if so where would I find details about how this spec was set?

Is this a spec for droop (potential shorting), strain (breakage during vibration), inductance, or something else?

Thanks,

John D

 

[lumenharold]

It has beed a while since I have had to spec a board with bonds (typically the vendor handles that) but we used to reference MIL STD 883 for pull requirements. I don't have a copy handy so I'm not sure there is anything there additional to help but this is a quick reference that might:

http://component-solutions.tek.com/...publications/MaxtekWireBondingArticle0706.pdf

We consider the potting material if the bond is potted as well as the environment when calculating max length.

Harold
SW2010 SP3.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
Dell 690, Xeon 5160 @3.00GHz, 3.25GB RAM
nVidia Quadro FX4600

http://www.lumenflow.com

 

[IRstuff]

Limitations of that sort are self-imposed:

http://component-solutions.tek.com/...publications/MaxtekWireBondingArticle0706.pdf

http://www.natelengr.com/documents/dg3wirebond.pdf

There are a number of reasons why one might limit the length, and you've mentioned most of them.
Some others:
> IR drop
> bonder limits -- You have move the bonder tip up and out to draw additional length, and then come back down. I can't really if there really a mechanical limit on bonders, though.
> damage to first bond -- drawing additional wire puts stress on the first bond

I vaguely recall seeing bonds longer than 0.1" but that was mainly due to putting a really small die in a package that was too large for it. And that was due to the fact that the large package was off-the-shelf, and the exercise was for a special test.

As to some of the concerns you raised:
> droop -- no necessarily a problem, since die are usually passivated, so shorting to the die is unlikely. Shorting to other bonds might occur if the loop height is excessive. Certainly, the longer the bond, the more sway space you should have allowed for in the bond pad layout.

> fatigue -- unclear, since the longer the bond, the smaller the angular deflection relative to the foot of the bond.

My guess would be that the most prevalent reason is inductance, particularly with high-speed, high-transient current devices. A poor bonding layout can result in several tenths of volts of bounce during a transient, enough to potentially change the logic state of the signal on the wire.

TTFN

FAQ731-376

 

[zappedagain]

I've seen the Maxtec article before. Unfortunately they only give typical values and no references to where they came up with the numbers.

The Natel link is interesting; I like that it gives a maximum length. I expect the clearance limits are tailored to their bonding equipment.

I'm thinking that fatigue may be an issue not due to the deflection angle, but due to the increased mass and thus the increased torque on the bond.

Thanks for the responses.

John D

 

[zappedagain]

I found that I had a copy of this paper:

http://www.amkor.com/index.cfm?objectid=4D4FDD20-5056-AA0A-E26C41696003A2B7

While it doesn't explicitly cover bonding, it does discuss the bond wire characteristics out to 5mm (0.197").

 

[IRstuff]

I'm fairly certain that there are many devices where the bond lengths exceed 0.1", since there was a gigantic mismatch in device I/O's vs. the ability to get them to a package in a conventional leaded package (J or gull-wing) in the recent past. That all pretty much changed with the introduction of beam leaded frames.

TTFN

FAQ731-376

 

[ScottyUK]

We routinely ran 0.001" bond wires out to at least 5mm, maybe 6mm, when I worked in thick film hybrids. Usually the long bonds were from package (ball) to substrate (fishtail) although we did have the occasional product with very long bonds from die to substrate. Those were usually the result of either: a designer trying to save the cost (and risk to yield) of an additonal gold print & fire layer; a die change; or a component substitution.

I seem to remember that some of the glob-top products had quite long bonds but it didn't really matter as it was encapsulated within minutes of bonding. Wasn't my line so can't be sure of lengths.


----------------------------------

If we learn from our mistakes I'm getting a great education!