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# how to determine the state of fuse resistor after taping out

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#### huashizng

##### Newbie level 6
there are three fuse resistor used in the trimming circuit of the bandgap voltage reference. if the chip is taped out, how to determine the state of three fuse resistor ? below is my guess, i don't know whether it is right.

three trimming bits bring 8 states. we can select 8 chips. we burn the fuse resistors with different methods. so the 8 chips have different state . we should determine in which state the bandgap reference voltage is most accurate .
so we test the value of bandgap voltage in different temperature.(maybe there exist a especial temperature instrument ) according these tested data, the chip owns the best, zero temperature curve is selected. so the fuse of the remain chips will be burned with this same method.

the above method is just my guess, i don't know whether it is right.
who can tell me the method used in practice?

Re: how to determine the state of fuse resistor after taping

ur guess is absolutely wrong! If u always select one combination,how to overcome the process deviation and parameter deviation,etc in different batch fabrication?
The purpose of trimming is to eliminate the effect of the process deviation and parameter deviation,etc. By different combination it can make the required parameter attain the designed typical value.
In another words,one goal is realized by many different combination, so the solution become flexible and easy!

Re: how to determine the state of fuse resistor after taping

huojinsi said:
ur guess is absolutely wrong! If u always select one combination,how to overcome the process deviation and parameter deviation,etc in different batch fabrication?
The purpose of trimming is to eliminate the effect of the process deviation and parameter deviation,etc. By different combination it can make the required parameter attain the designed typical value.
In another words,one goal is realized by many different combination, so the solution become flexible and easy!

So does it mean for each lot of wafers has its own trimming combination?

Or, can I say that, huashizng method can still be used. However, it is used in lot by lot base rather than just choosing one set of trimming combination for different lot of wafers.

Thanks
Scottie

Re: how to determine the state of fuse resistor after taping

which method can we use to decide the trimming state in practice?
whether the method i have suggested above can be used to trim every chip respectively?

Re: how to determine the state of fuse resistor after taping

Hi

Trimming can be done either lot by lot or wafer by wafer or even die by die, but it depends on the accuracy requirements and affordable costs.

Please correct me if I am wrong. Thanks!

regards,
jordan76

Re: how to determine the state of fuse resistor after taping

scottieman wrote:
So does it mean for each lot of wafers has its own trimming combination?
Yes. for different lot of wafers it will have its different trimming combination.
huashizng wrote:
which method can we use to decide the trimming state in practice?
Which trimming state is choosed, it depended on the soft program of chip probe instrutment.The soft program can judge which combination.
whether the method i have suggested above can be used to trim every chip respectively?
ur suggested method can be used to trim some chips,but not every chip!

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