Hi Inge-
No, no requirement for "half moon crescent", other than, if you have good pulltest data, the flameoff process is working well, and the underlying pad you are stitching to isn't damaged, then probably you will have a nice crescent.
No, never used Manson. We encapsulate or overmold everything we make, so vibration isn't an issue. And if repetitive thermal cycles are the problem, then I suspect that the intermetallic areas are more likely going to fail first. As a matter of fact, once predicted failures go out more than 20 years, a whole bunch of low probability of occurrence stuff has a chance to happen!
Was the stress you analyzed due to vibration? You mention Kovar and alumina, but I thought those were supposed to be matched closely enough that rates of thermal rise and thermal conductivity are more important than linear coeff of elongation.
Wayne
-----Original Message-----
From: Inge [mailto:[log in to unmask]]
Sent: Wednesday, June 16, 2010 4:54 PM
To: Thayer, Wayne - IIW; [log in to unmask]
Subject: Re: [TN] ?
Thanks Wayne.
1. No aspect on 'half moon crescent' ?
2. Have you or someone else practised Manson's universal slope equation
for calculation of life expectancy of bond wires?
Delta epsilon = 3.5 x sigma b/E x Nf exp-0.12 + epsilon1 exp 0.6 x Nf
exp -0.6
where
Delta epsilon = elongation
sigma b = rupture tension
E = elasticity module
Nf = number of cycles to rupture
epsilon1= rupture elongation
We used this for deciding how many cycles gold wires would withstand in a
typical MIL aircraft application when the substrates were alumina and the
packages Kovar. The result was som 50,000 - 100,000 cycles or 60-120 years
for -55/+125C.
The question is how much one can rely on this calculation model. Anyone
done similar ? Personally I thing one should only see such calculations as
estimations only.
Inge
--------------------------------------------------
From: "Thayer, Wayne - IIW" <[log in to unmask]>
Sent: den 16 June 2010 20:57
To: <[log in to unmask]>
Subject: Re: [TN] ?
> Hi Inge!
>
> 5 grams per square mil average shear for gold ball bonding
> Avg - 3 x StdDev > 3 grams for 1 mil gold destructive pull test
>
> The latter is kind of vague because the wire set must be large enough to
> get a good sample size and all of the loops have to have reasonable
> heights and must be similar.
>
> For aluminum, we're very application-dependent, but use the Avg - 3 x
> StdDev as the parameter of interest.
>
> These don't test how close to cratering we are, which is an industry-wide
> issue.
>
> Visually, we are looking for a consistent rim on the ball, and a rim
> height no greater than about one half of the wire diameter. For the
> stitch, consistency and virtually no capillary imprint from the stitch
> process on the lead/land.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Wednesday, June 16, 2010 1:58 PM
> To: [log in to unmask]
> Subject: [TN] ?
>
> What standards do you use for inspection and qualification of wire bonding
> today?
> Thanks
> IInge
>
>
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