Develop a robust process
In today's competitive environment, there is no room for delays and errors.Your marketing analysis is complete and your strategy honed but you still have to put your product on the market. You will have to run an efficient process to get an edge on the competition.
Getting an experienced development team together is difficult when pioneering new grounds. The alternative is to develop experience in house, which takes time and money and delay your increased sales. We can provide the technical guidance that will allow your team to get faster results.
Choosing new polymer materials from dozens of products offered on the market is not an easy task. All sales literature and presentations look good, at least on paper. Finding or adapting a metallization scheme to a new material and developing an RDL has some long range implications on the company viability. Identifying the correct new equipment needed with minimal chances of error can be very difficult.
We provide help to develop a robust metallization scheme for RDL and UBM, streamline your photolithography or help etching or plating your conductor lines. Although semiconductor manufacturing and WLP thin film processes have many similarities, there are many critical differences. Processes and procedures that are a necessity for submicron work may bring an insurmountable burden on a backend process and irremediably ruin its profitability.
Sputtering is at the base of all WLP processes, additive or substractive. Depositing a thin plating-base places a light burden on the equipment; on the other hand, sputtering thick layers of conductor on polymers can be frustrating with the wrong sputtering machine. To achieve acceptable RDL electrical properties, the metal thickness needs a substantial increase over the time honored one micron thick aluminum used in ICs. The RDL metal is sputtered over a thermally insulating polymer layer that deeply affects the morphology of the films and produces very different results than sputtering over a silicon wafer which has orders of magnitude, better thermal conductivity even in the presence of a one micron thick film of SiO2 or Si3N4. Pumping systems, target configuration, mechanical handling system, computer control software can make the difference between a barely acceptable machine and a productive reliable one.
Photolitho for WLP and other advanced packaging applications, is quite different from contemporary submicron photolithography done on wafers. The similarities end at the fact that they both use photoresist and light to define features. The minimum line width and space required to build WLP is similar to the requirements placed on photolitho, when early integrated circuits were built forty years ago. Choosing the right equipment, materials and processes can make an enormous difference in productivity and yields.
Wet etching is often perceived as applying low-level kitchen recipes using mysterious commercial concoctions. This confirms that often the chemistry and electrochemistry involved in etching is poorly understood. It surely can be quite complex, particularly when several layers of different metals are in contact with the etchant. Because high-end interconnect lines need precisely controlled cross-section and dimensions, etching multilayer metal sandwiches can be pushing the limits of substractive processes.
Electroplating can provide better geometrical control in high volume, as demonstrated by 25 years of magnetic thin film heads production. Electrolytic deposition of copper between walls of photoresist or polyimide can provide better and more economical interconnect than thicker etched sputtered films.
The most frequent use of plasma etching in WLP is the removal of the unavoidable and frustrating scum left behind most (not all) polymers after development. There are many more untapped applications, particularly in etching adhesion or barrier metals. Barrier metals are used because of their resistance to chemical attack and physical stability. Unfortunately, the same qualities that make them desirable as diffusion barrier imposes the use of aggressive chemistry to remove them. These aggressive etchants can wipe out surrounding materials. Fortunately, some adhesion and diffusion barrier metals form gaseous products in a plasma, leaving the surrounding materials untouched.