Wafer Sawing
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
- Our precision saw allows us to saw completely through wafer on film
- Wafers are cleaned by nitrogen/de-ionised water rinse wafer washer
- We can saw wafers up to 8" / 200mm in size
- Automatic handling
- Single or part wafer flexibility
- Sawing of customers own product