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

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

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

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

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

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

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

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

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

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

WaferScan Setup OD normal behavior Number of Failed Pins 30 40 50 55 60 65 70 75 OD [mm] DCG Confidential

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

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