Let us take a look at some of the recent applications, such as opto-electronics and stacked die packaging where wire bonding has been used. By understanding the demands made by these new packaging applications, one can appreciate the criticality of understanding the wire bonding technology and its importance in the “food chain” of microchip manufacturing and more importantly in the electronics vertical.
Wire Bonding in Opto-Electronics
Even today, choosing and designing a packaging technology for a device is often undertaken late in the game and without an appreciation of its difficulty and its potential effects on the final product performance and reliability. However, in optoelectronic applications, packaging accounts for roughly 60 to 90 percent of the cost, and much of the cost is related to low yields in manufacturing. Therefore, a significant amount of stress is given to the packaging issues both from design and manufacturing perspectives.
A typical opto component consists of substrates, sub mounts, heat spreaders, optical components, amplifier ICs, detectors and most importantly the optical fibre, as shown in figure below. The precise placement and alignment of the optical components are the most technically challenging. The other key technology in optoelectronic manufacturing or photonic component manufacturing is wire bonding. Here the challenge lies in bonding to multiple surface metallization within the same package, large bonding height differential and low bonding temperature.
There are many types of opto packages including LTCC packages (Low Temperature Cofired Ceramic), Photo Patterned Thick film package, and plated copper on ceramic, direct bonded copper and thin film substrate packages. Each of these packaging technologies have different kinds of metallization which necessitates choosing the either ultrasonic Al wire bonding or thermosonic Au ball bonding, and optimizing the wire bonding technology for each package.
One of the greatest challenges in wire bonding an opto package is the height differential between different components in the package.