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In order to achieve
maximum efficiency with the use of ultrasonic wire bonding, the die,
the package and the wire must be compatible with the bonder as well
as each other. Here we will show some guidelines to be followed.
Material
The material we are talking
about are those materials that are in direct contact with the wire. There
are some materials that will not bond to aluminum wire no matter how much
care is taken. There are also materials that can produce good bonds under
certain conditions and usually the quality is dependent on the purity of the
material or the process to which it is applied. Materials that are
recommended for ultrasonic wire bonding are those that have always produced
good results.
|
Selected Bond Pad Material for
Aluminum Wire |
|
Best |
Conditional |
Poor |
| Aluminum |
Palladium Silver |
Tin |
| Nickel |
Palladium Gold |
Kovar |
| Gold (Plated) |
Platinum |
Stainless |
| Gold (Thin Film) |
Platinum Silver |
Solder |
| Copper |
Platinum Gold |
Iron |
| Silicon |
Gold (Thick Film) |
Ceramic |
| |
Metal on PC Boards |
Brass |
| |
|
Plastic |
| |
|
Anodized Aluminum |
| |
|
Constantin |
| |
|
Silver |
| |
|
Zinc |
| |
|
Carbide |
Wire specifications
The next step in designing a product is to
determine the amount of current to be carried through the device. Once the
current is known, the minimum wire size is easily derived through a formula.
Bond pad considerations
After the wire size is known the next step is to
design the die to accommodate the wire. The width of the pad must be twice
the diameter of the wire and the length should be between 3 to 3.5 times the
diameter of the wire.
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