Over time, PCB manufacturing has evolved from the traditional through hole, to through hole combined with SMT, and today, a growing number of PCBs are assembled with a combination of SMT and microelectronics or bare die wire bonded onto a substrate or the PCB, itself.
Die attach is an integral part of microelectronics. In 2019 and going forward, microelectronics will play a vital role due to the fact today’s advanced electronics is shrinking PCB real estate. PCBs and components are decreasing in size and becoming increasingly delicate. Thus, it’s growing ever more difficult to assemble, inspect, and test a product.
For example, many of these smaller PCBs cannot go through a traditional PCB assembly and manufacturing line. A growing number of these boards must undergo specialized microelectronics packaging involving wire bonding and die attach.
Check out our article on EEWeb for more details. In the meantime, here are some tips and hints to get you started on better understanding PCB die attach.
- Dies are typically on a tape, in a wafer, or in a waffle tray.
- Die attach begins with target tide picked up by a small vacuum suction tool from either a waffle tray or a wafer pack, Fig. 1.
- Die attached uses one of three methods, epoxy, eutectic, or solder attach.
- Epoxy bonding could involve silver epoxy glass or be based on a polyimide material.
- Extremely precise dispensing is critical for die attach.
- Eutectic die attach also called flux-less solder attach process and uses a thin metal layer called preform comprised of gold-silver, gold-tin alloys or something similar.
- Solder attach is a common type of die bonding due to better thermal conductivity of the solder material.
An important aspect of solder attach is that the die needs to be fluxed. Before that is performed, the initial solder alloy needs to be pre-plated over the die metallization and the substrate metallization. If a certain layer is needed, it will require a slightly different composition of die and substrate. Once that is performed, the die is placed on the substrate using the die placer. Afterward, the die must be cleaned before that it is encapsulated.
It’s also important to know that flux-less solder can be used for the solder attach method. Here, a wire is fed into the system where it is pre-heated. It then melts the solder, and the joint is formed.
Die attach is becoming a more prominent technology for small PCBs like rigid and flex circuits. It’s important for OEM designers to get a good handle on the three types of die attach methodologies suitable for their applications.