Wafer sawing - The concept

There are several forms which the customer may prefer to receive their end product, for example, waffle pack, gel-pak, wafer sawn on ring-frame etc.  For each case in order to convert the wafer into a useable form it must be sawn.  Due to the delicate nature of the raw material, consideration must be given to several factors which effect the overall yield and quality of the separated die.  Factors such as blade speed, cutting patterns, or even the electrical charge carried by the filtering water used can have a significant impact on the output of the sawn dice. There is also a great deal of both skill and experience associated with wafer sawing as products can vary significantly in both their size and composition material.  E.g. A silicon saw process would be very different from a Galium Arsenide process.   

Wafer saw - The process

Before sawing can take place the wafers must be mounted onto a ringframe.  This is achieved by use of a mounting chuck which stretches a specialized foil across the backside of the wafer. The foil is roll-pressed to ensure even coverage across the wafer's backside surface and the excess foil is then removed.  An important factor to consider at this stage would be the die size in relation to the resistivity factor of the foil. Once the wafer is suitably attached to the ring frame it is ready for sawing.

The wafer on ringframe is then secured on the moving saw chuck where it's position is then sensed and calibrated by the saw's internal configuration program.  The configuration program automatically presets the saw's X and Y co-ordinates to follow the wafer streets (empty tracks between each die).  This automated handling of the wafer enhances accuracy and reduces the likelihood of human error.  After the wafer position is calibrated the actual cutting occurs by moving the chuck into contact with a rapidly spinning diamond stud blade which is mounted on a spindle above the wafer.  The saw moves and rotates the chuck in accordance with its program until all streets have been cut.  The wafer on foil is then removed, washed in a specialised solution and then dried via infra-red in order to remove remnants of raw material dust from the saw process.

Foil and Tape - The process

Most die that are shipped on tape only have a short shelf life (average three weeks) before the tape deteriorates. The tape will start to lose adhesion allowing die to fall off in transit or at the pick and place operation, in addition with longer life the adhesive strength will increase on the tape making the die difficult to remove and will contribute to back surface rejects.
At Ditech we use a tape that if stored correctly at room temperature will release the die at a consistent force for a period of 10 years. This allows long term storage, eliminates damage on removal and speeds the pick and place rate.

Wafer saw - Equipment / Capabilities

Up to 8 inch / 200mm

• Automatic handling

• Single or part wafer flexibility 

• Sawing of customers own product