This assembly went through the laser scan test on 13-Dec-99 and two channels(193,254) of this assembly were idenfied as dead.

Fig 1. Pedestal of each channel

Fig 2. Result of the laser scan.

On 6-Jan-2000 bench cal test has been done about these dead channels. The result was the same with the MCM test result. Two channels were still O.K with the bench cal test. I think this means wire bonding causes the dead.

In Fig 2. there is a fluctuation of the adc value through different channels. I think the most part of this fluctuation is coming from variation in the laser focucing for each channel. In the meantime, a interesting behavior around dead channels was found during the QA test. If the laser hits the dead channel, the adjacent channels of that dead channel tend to be excited,i.e show rather big ADC value above the pedestal. This effect produced about 40 ADC ch(average value) above the pedestal on channels around the dead channel when the laser hit the dead channel, while the direct hit of the laser on those channels produced about 160 ADC ch(average value) above the pedestal. But this is not true for all dead channels of different assemblies. I don't know whether this effect will be significant in the real experiment.

last modified Jan-26-2000
YoungGook Kim