1. WaferScan Probing & Contact Process Differences from Sort Floor Probing Izak Kapi Kapilevich Aug 2013

2. Wafer Interaction with Probe Card (PC) and reaction to Overdrive (OD).
Outline
Wafer Interaction with Probe Card (PC) and reaction to Overdrive (OD).
Proper Overdrive (OD) Behavior & Setting
What to test if full contact cannot be made
DCG Confidential

3. Production Sort Floor Prober Setup
Pogo Array Ceramic
Housing
Pogo array is in first contact but
as you can see not all pins contact
Prober Chuck Solid Surface
The Pogo pins are not all equally distributed in Z, even on a new PC. Lets call the Z difference as PCDZ
Some OD is required to make sure the shortest pins contact the wafer
The OD is typically small - just enough to overcome pin height variations in the order of 10mm to 40mm
Additional OD may be necessary to insure good electrical contact
DCG Confidential

4. Production Sort Floor Prober Setup
Pogo Array Ceramic
Housing
Probe Card is now in full contact
We will call probe OD as POD
Prober Chuck Solid Surface
The Pogo pins are not all equally distributed in Z even on a new PC that is why we need OD.
Additional OD is also needed to ensure good electrical contact with low contact resistance
DCG Confidential

5. WaferScan Setup PC Not Landed
Pogo array
Same consideration
Applied for Cantilever
Pogo Array Ceramic
Housing Z
Z height difference
between pins is important
The Pogo pins are not all equally distributed in Z even on a new PC
When the platen is in retract position there is no contact with the wafer. The wafer is flat held by vacuum chuck
The illustration in this example is shown with a 20X Air Gap Lens
DCG Confidential

6. WaferScan Setup PC First Contact
Pogo array is in first contact position
Some pins are in contact but note some are fully open
Note: That if OD is zero there is no wafer bow.
The Pogo pins are not all equally distributed in Z so some pins have already made contact but some are still open.
OD must be at least as much as the Z distribution of the Pogo Pins height variations in order to make full contact (PCDZ).
OD must be higher to make a good contact as each pin requires some down force to make the contact good.
DCG Confidential

7. WaferScan Setup PC Full Over Drive
Pogo array is in full contact position with an OD that needs to
Overcome pin force and wafer bow.
Note the wafer is now bowed by 50mm which makes the
Center pins press less then edge pins
The Pogo pins are now all in contact with the wafer however the wafer in the center of the die moves down so the pogo pins in the center are not pressed as much as the pogo pins in the edges.
The wafer bow can be up to 50mm or more so the pogo pin compression varies between die edge and die center.
DCG Confidential

8. WaferScan Setup PC OD setting
The important parameters we need to make sure we understand are:
PCDZ
POD
Wafer Bow as a result of pin PC pressure
The PCDZ is known and usually given by the PC spec sheet or can be measured using the WaferScan InGaAs Camera and 20X lens.
POD is the Over Drive Used on the prober
Wafer bow is typically about half the Over Drive used. For example if OD is 40mm the wafer center will move 20mm lower. This is true for any PC with over 500 pins. This may be slightly lower for a low pin count PC.
DCG Confidential

9. WaferScan Setup PC OD setting
Specific example using Eagle wafer and PC in Samsung
POD is 40mm,this OD is needed to overcome the PCDZ
On WaferScan starting point should be the same OD as the prober so 40mm is the starting point.
We need to take into account the wafer bow and think about effective OD. If we use 50mm OD the wafer will bow 25mm so the effective OD for the center pins is only 25mm.
That is the reason contact is unstable at 50mm OD because the PCDZ and the wafer bow cause some pins to barely contact.
DCG Confidential

10. WaferScan Setup OD normal behavior
There are some indicators that OD is behaving as expected and we can increase OD without worry of wafer or probe card damage.
If first contact is set correct the wafer bow is usually about ½ of the OD
As we increase OD the number of failed pins decreases. As long as this is linear behavior we know we are on the right track for making full contact.
If after increasing OD several time there are always 1 or 2 failed pins we need to check the pins, run TDR, inspect the PC and test it and finally check the interface.
On the next page a plot to demonstrate the linear behavior of proper contact
DCG Confidential

11. WaferScan Setup OD normal behavior
Number of
Failed Pins
OD [mm]
DCG Confidential

12. WaferScan Setup OD normal behavior
There are cases when changing Lens (Magnification) can cause contact disruption and in those cases a simple recovery is needed.
If an Air Gap is used (1X, 20X or 50X) simply retract and re-land the probe card.
If SIL lens is used we need to do a second SIL landing (Kapi’s Landing) as the following steps describe:
Move the SIL down 100mm by using the Z motion
Retract probe card
Land probe card
Move SIL back to get Focus but do not use AF and do not move up in 1 step of 100mm use steps of 5mm to slowly move SIL to focus.
DCG Confidential

13. Summary
The key parameters that influence WaferScan Probe Card Landing are:
Probe Card Pogo Pins/Needles height variation
The Overdrive required on the prober
Wafer interaction with probe card that causes wafer bow
Does the Overdrive and failed pins relation show a linear improvement
Wether or not we are using Air Gap Lenses or SIL may have some impact and requires testing the continuity after SIL has made contact with the wafer and image is in focus.
DCG Confidential