In most cases, the operator of a die bond (or pick-and-place) machine will have a wafer map for each wafer to process. The map determines which die are picked and which are skipped. Die may be skipped for a number of reasons: they test electrically bad or they are close to the edge of the wafer and have been marked as "ugly" or "edge".
However in some situations, wafers are received without a wafer map. Why?
For certain types of devices -- say RFID chips -- the die size is very small and the yield is very high. Due to the small die size you might have more than 300,000 good die on a wafer. Testing that many die might not be cost effective.
Figure 1: A 150 mm diameter wafer. Die in "blue" are to be skipped.
However the pick and place operator still needs to program his die bonder which can be done manually or by importing a wafer map. Since the wafer was not probed there is no wafer map. And with > 300K die, manual programming is slow.
A map can be generated using a utility available as part of WMapEdit. This utility allows the user to enter the wafer diameter, a margin a flat distance and the die size. From that information a map can be generated that marks all of the die that should be skipped with a unique bin code.
Figure 2: A wafer map can be generated using the following geometric inputs.
In this example we will generate a map that excludes all edge die using the following geometry.
| Wafer Diameter: | 150 mm |
| Wafer Margin: | 4 mm |
| Wafer Flat: | 9 mm |
| Die Size: | 0.225 x 0.255 mm |
Start by opening WMapEdit and selecting the Tools drop down. Select
The Synthesize Wafer Map dialog box will open. Enter the values from the table above. Define the Bin Codes you want to use for pick die (enclosed) and skip die (margin).
Now press the OK button and your map file will be generated and displayed on screen. In a second or two you should see your map displayed.
Notice that WMapEdit shows the count for each bin: 308,154 die are to be picked, 42294 die are to be skipped. The rest are null positions needed to keep the array square.
You can download the sample SINF file here:WmapEdit-Synthesized.sinf.zip 10K zipped.
With WMapEdit, one can zoom and pan throughout the wafer map. This is essentially for these very large maps where you cannot clearly find things at full magnification.
In the image above you can see that the die highlighted in red is located at position 553,560 in the array (measured from the upper left) and at 49.3411,-50.9054 mm measured from the wafer center.
After testing we've determined a number of additional features would be useful to customers. These include:
OFFSET
The center of the wafer map does not usually correspond precisely with the center of the wafer. If the user knows the "offset" this could be another input parameter. Shifting the map center often changes the total number of enclosed die.
Deleting Zones inside the Enclosed Area
Many of these wafers have a number of "zones" in the enclosed area that should be skipped because they contain test die or other non-pickable features. We will add a method to list these "zones" (by physical coordinate or array coordinate) to allow a user to quickly change the bin code in those zones.
Adding Alignment Die
While alignment die can be identified once the wafer is on the machine, it may be more convenient if the position is known, to edit the wafer map off-line.