Testing
Description:
After a bonding task is finished, the next step is to test the part and identify the faults. We currently have the following categories of identifiable DFA faults (the description of the methods used to identify the faults assumes that the bias voltage supply is not current limited):
1. Pinholes (break through the oxide layer):
The most decisive test of whether a fault is a pihnole is thePinhole Scan, where pinholes draw about 1uA of current when a +5V voltage is applied, and, on the phi side, they also draw a large current when (if) -5V is applied.
In theCs Rs Scan, they usually appear as having larger than usual Cs and Rs.
2. P-stop shorts, Phi side only (break through the oxide layer to implant)
- Again, the most decisive test of whether a fault is a p-stop short is the Pinhole Scan, where p-stops draw about 20 uA (the current limit) when a +5V voltage is applied, and a very small current when (if) -5V is applied.
- In the Cs Rs Scan, they can have varied Cs and Rs (including normal values).
3. Shorts to readout strips (ROS-shorts, caused by leaning wirebonds, shorts or metal flakes on the Upilex, metal shorts on the silicon wafers, etc..)
- In the Pinhole Scan, they draw about 20 uA of current (the current limit) for both +5V and -5V of applied voltage.
- In the Cs Rs Scan, they have about twice the Cs of normal strips, and about 1/2 the Rs of normal strips.
- In both the Pinhole Scan and the Cs Rs scan they appear in groups of two or more.
4. Shorts to floating strips, Z side only (shorts between read out strips and floating strips, usually caused by bond feet being a little off center on the silicon, and touching the floating strip)
- They do not appear in the Pinhole Scan.
- In the Cs Rs Scan, they look very similar to ROS shorts, but they can be by themselves (while ROS shorts always appear in groups), and the value of Cs is a little smaller than that for the ROS shorts.
5. Low capacitance and Opens (caused by a missing wirebond, a broken trace on the Upilex, broken metal on the silicon, etc..)
- They do not appear in the Pinhole Scan.
- In the Cs Rs Scan, they have lower than normal Cs (which may be also caused, for example, by the probe missing the tree on the Silicon).
- If there is a missing Silicon to Upilex bond, or a broken trace on the Upilex, which we can confirm visually, then this is an Open. Otherwise, it's Low Capacitance.
- If there is a missing butt bond, it's still Low Capacitance (it's not completely open, since the strip on wafer 1 is still connected).
Testing Sequence:
- Position the part on the probe station copper plate according to its layer, direction, and side (e.g., "L3FZ" marks on the plate are for layer 3 forward DFA's, z side up). Connect the bias connector, and close the lid.
- On UCSB5, click on theMain###.llb icon in the row of SVT lab icons normally displayed in the right hand corner of the screen, which will open Main Control vi automatically.
1). The first test to be run is the Cs Rs scan, which measures interstrip capacitance (Cs) and resistance (Rs). Select "Cs Rs Scan" in the "Test" window in the upper left hand corner of the Main Control panel.
- Settings
: Start Strip, End Strip, and Bias Voltage should be set automatically for a given part.
Voltage = 1V.
Frequency = 100Hz.
- Things to look for
: this test can see open channels, whereas the Pinhole Scan cannot. If there are a lot of opens found in this test, it could be a sign that the probe is missing the Upilex trees.
- After the test is finished
: print out the front panel of the vi if it was not done automatically. Put it together with the Bad Channel List (which should also be printed out automatically) in the part's binder.
2). The second test to be run is the Pinhole Scan. Select "Pinhole Scan" in the "Test" window in the upper left hand corner of the Main Control panel.
- Settings
: Start Strip, End Strip, and Bias Voltage should be set automatically for a given part.
Test Voltage = 5V
"+ and -?" switch = ON for Phi side testing, OFF for Z side.
"Plus Shorts" Button pressed.
- Things to look for
: if the bulk detector current (lower left hand corner of the Main Control window) increases when the probe contacts the part, that usually means that there is at least one p-stop short on a strip that the probe is contacting. If the bias supply current limits (about 20 uA, and the "Operate" light on the voltage source flashes), then the test results may not be easy to interpret. In particular, the Bad Channel List that gets printed out at the end of the scan may not have diagnosed some of the faults correctly.
- After the test is finished
: print out the front panel of the vi if it was not done automatically. Put it together with the Bad Channel List (which should also be printed out automatically) in the part's binder.
After testing is done, enter the corresponding entry into the DFA database!
The data from a given test should be located in \\ELECTRON\babar\svt_lab\DfaTests\DataLogs\, under the part directory (e.g., for D02B.10 the directory will be d02b10). There should be a directory there called r###### (r stands for "run", and the 6-digit number is the run number which is also displayed on the front panel of the Main Control vi during the run). This directory, in turn, should contain four files: r######.cur (bias, guard, and total currents), r######.dat (data depending on the test), r######.env (temperature and humidity), and r######.inf, with some information about the run.
People to ask if problems arise:
Doug Roberts
Philip Hart
Sam Burke
Jeff Richman