The industry is increasingly moving toward PCB hybrid assembly involving both traditional SMT and microelectronics assembly and manufacturing. Using the right type of glob top epoxy represents one item that can be easily taken for granted and overlooked during microelectronics manufacturing. Fig. 1 shows an example of a clear epoxy glob top.
These are the epoxies used for die attach and wire bonding during PCB microelectronics assembly. A basic rule of thumb to keep in mind is that glob top epoxies are not created equal.
There are multiple manufacturers producing different types of epoxies. And even within each manufacturer, there are multiple and different types of epoxies being produced. Another key point is that EMS providers and contract manufacturers generally are the ones deciding on the kind of epoxy to use, depending on a specific application.
Therefore, prudent OEMs launching newer and smaller products like wearables, IoT devices, and other portable gear should get a good understanding of glob top epoxy basics.
For more details, check out our SMT007 Magazine article. In the meantime, here are some tips and hints:
- Epoxy is composed of different characteristics or elements. Some may have adhesive characteristics; others may have conductive thermal characteristics, but non-conductive electrical characteristics, depending on the applications that are being used.
- A good epoxy should display low thermal stress during temperature cycling.
- Understand the epoxy’s curing process because it is dependent on an epoxy’s application. Curing means the epoxy goes through a cycle of a specific temperature range, which is for a certain time interval.
- Process engineering on a PCB microelectronics assembly line should closely inspect viscosity. It is one of the most important epoxy characteristics that will either make your project successful or a failure.
- Epoxy dispensing methodologies and techniques also play a critical role in epoxy dispensing.
- Understand there is a distinct amount of epoxy dispensing time when attaching a die. Otherwise, it’ll dry too quickly.
Also, for glass-transition temperature (Tg), what is important to know is that high glass transition epoxy compounds are critical to the adhesive selection for higher temperature applications. These products have superior mechanical, thermal and electrical properties than lower Tg materials at high temperatures.
You have to take into consideration the Tg as a major factor when choosing the right epoxy for your given application. For example, an application may require a flexible epoxy. Therefore, a low Tg or a level below 0°C is acceptable for that application.