There is no big secret. PCB manufacturing is changing now more than ever before in its long history. Initially, it involved through-hole assembly and manufacturing with the most notable Intel 8086 motherboard. Later, through-hole and surface mount technology (SMT) began merging and sustained a long product cycle.
But today, PCB manufacturing is rapidly evolving to include SMT as well as microelectronics, such as chip-on-board (CoB) installation, flip-chip assembly, wire bonding, and die attach. SMT merged with microelectronics is also known as hybrid manufacturing (Figure 1). This is occurring because PCBs have begun shrinking at a faster pace in recent years due to the introduction of wearables (i.e., medical, commercial, and aerospace industries), IoT devices, and portables demanding smaller circuit boards.
Figure 1: Hybrid manufacturing.
PCB assembly and manufacturing continue at a high rate to use small rigid, flex, and a combination of rigid-flex circuit boards to comply with OEM product requirements. When you have such small boards, you then have to rely on newer methods and technologies on the SMT floor and in cleanrooms. At the same time, you have to adapt your thinking away from SMT and more into the intricacies of microelectronics, also known as wire bonding.
Wire bonding is not new since it has been used since the early transistor days. But now, there are newer techniques that must be mastered and applied for SMT/microelectronics manufacturing. There are different wire bonding methods and different types of wires, gold, aluminum, silver, and more. Each type and method must be carefully evaluated for the right application. If poorly chosen, the OEM customer could incur poor performance or failures in the lab or the field at a later stage.
Savvy OEMs with wearable, industrial IoT devices, and other portable products should start familiarizing themselves with PCB hybrid manufacturing. It’s a new world involving not only different wire bonding but also the integrity and reliability of each type of wire bonding. Also, understanding the best methods for die attach is crucial because you want to use the correct method, whether it’s epoxy, eutectic, or solder attach. Each has its merits for certain applications, and it is crucial to know and understand.
Also, some components used in microelectronics have different coefficients of thermal expansion (CTEs) compared to traditional SMT components. This aspect needs to be carefully evaluated and verified so that when SMT manufacturing is performed, it doesn’t adversely affect the microelectronics portion of the assembly.
One has to keep in mind that traditional SMT components undergo unleaded or lead-free assembly with fluxes and pastes conducive to SMT manufacturing. However, when it comes to microelectronics, there may be different epoxies with various chemical compositions. That’s when thermal profiles with different aspects come into the picture. Keeping the thermal profile intact and in the right place is highly critical. The reason for this is components expand and contract at various temperature cycles. Contraction and expansion are at different rates for traditional SMT components compared to microelectronics components.
Also, component placement and its design during layout are most important, depending on board size and packages populating the PCB. The reason for this is you want to keep analog and digital components separate because analog typically operates at a higher current and with more heat compared to their digital counterparts. Similarly, care must be taken when SMT and microelectronics are merged together on a PCB regardless of its size. This ensures that SMT/microelectronics component placement is easy for different manufacturing tools to physically reach certain areas to perform microelectronics manufacturing and assembly after SMT manufacturing is completed.
Again, hybrid manufacturing is a major industry endeavor. It’s critical for existing and new OEMs launching into the next round of small PCB designs to gain a clear understanding of all the upcoming manufacturing technologies supporting new products. It is especially important to place extra emphasis on microelectronics manufacturing and its requirements for absolutely clean surfaces so that these assemblies are properly performed without jeopardizing reliability.
Zulki Khan is the president and founder of NexLogic Technologies Inc.