Multiple touchdown method - the way to high UPH


TWO WAYS TO TEST WLCSP MEMS

1. Single touchdown method - common practice

Single touchdown method is the only possible way to test MEMS with traditional gravity handlers and pick&place handlers
Testing is carried out by loading of certain group of DUTs to stimulus unit -> execute all tests for DUT group -> unload -> load of new group of DUTs

Figure Single touchdown method with Pick&Place handler
UPH example: 3-axes accelerometer, 16000 DUTs, 32 parallel, 4 stimulus points, zero test time)



2. Multiple touchdown method  - a new way to test
Multiple touchdown method is suitable for probers with physical stimulus such as KRONOS and AIOLOS.
Testing is carried out by loading a wafer ring(film frame) to prober  -> set stimulus -> probe all DUTs -> set stimulus -> probe all DUTs  -> when all the DUT’s are measured in one stimulus point, the stimulus is changed and the contacting moves again to the first DUTs -> probe all DUTs ... unload wafer

Figure Multiple touchdown method with Prober using physical stimulus
UPH example: 3-axes accelerometer, 16000 DUTs, 32 parallel, 4 stimulus points, zero test time) 




WHY DOES MULTIPLE TOUCHDOWN METHOD GIVE SO MUCH MORE UPH?
 
1.     The time is used for testing, not for loading and unloading.
Film frame easily contains > 10 000 DUTs. These are loaded to prober in one loading when using Multiple touchdown method. .Loading of 32 DUTs at the time, when using Single touchdown method requires several hundreds of Load/Unload sequences during which the test handler is down.

 
2.    Stepping is fast compared to stimulus change
In the previous example the rotation time of P&P handler was considered same as the stepping time of  the Prober. Typically this is not the case, but stepping is much faster than changing stimulus. Especially in pressure sensor testing, changing of pressure takes lot of time before it stabilizes to accurate value. By keeping the pressure value constant and stepping through all the DUTs leads to significantly higher UPH. The same applies also to gyroscope testing. With single touchdown method there will be hundreds of accelerations and decelerations, which take lot of time. With multiple touchdown method the prober can spin in constant yaw rate very long time.

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