Tech companies are talking about designing IoT devices with AI and machine learning. Before getting there, IoT device OEMs must take a couple of steps back and assure themselves of effective printed circuit board microelectronics assembly and manufacturing as an initial step to assure product integrity and reliability.
An item such as using the right epoxy during printed circuit board (PCB) microelectronics assembly might sound mundane to less savvy PCB assembly and manufacturing engineers. An inexperienced process engineer on the assembly floor might just shrug it off during the epoxy selection process and inadvertently chose the wrong one. That leads to the highest probability of subsequent product failure or delayed latent field failures.
Therefore, it’s a good idea for IoT device OEMs to get a good handle on the what, how and why roles associated with epoxy.
An epoxy is used on the bottom of a bare die and its wire bonding on an IoT device substrate or PCB to protect it. However, a main point to be made here is that not all epoxies are created equal. There are multiple manufacturers producing different epoxies. And even within each manufacturer, there are multiple types of epoxies being produced. Also, it’s important to know that Enhanced Messaging Service providers and contract manufacturers are generally the ones deciding on the kind of epoxy to use.
Selecting the right epoxy for your IoT PCB product involves epoxy characteristics, curing conditions, viscosity and glass-transition temperature.
Epoxy characteristics. Epoxy is made up of different elements. For example, some might have adhesive traits while others might have conductive thermal characteristics. However, some don’t have non-conductive electrical characteristics depending on the applications that are being used. When it comes to temperature, an epoxy should be effective at different ranges, allowing it to be used with different substrates and surface finishes.
Curing conditions. Curing is dependent on an epoxy’s application. Curing means the epoxy goes through a cycle of a specific temperature range during a specific time interval. Some epoxies are cured at lower temperatures, and others at higher temperatures. Some are cured in minutes while others take an hour and a half to two hours.
Viscosity. This is important because different IoT PCB applications require different viscosities. If the viscosity is not right — meaning it is too thin or too thick — it can cause issues during application. If it’s too thin, the epoxy will spill out to the outside periphery of the die, thereby creating unstable die attach joints before wire bonding can be performed.
Dispensing the epoxy itself plays a critical role in an IoT device’s reliability. Here, the accuracy of the epoxy lines dispensed under the die for die attachment is highly important. Also, the dispensing methods are extremely important. Each one, whether it’s a pump, needle or syringe, must be carefully evaluated for a particular die attach application.
Tack time is closely associated here. There’s only a certain amount of time allowed to attach a die. Otherwise, the epoxy can dry too quickly, which leads to a die attach that is not optimal.
Glass-transition temperature (Tg). 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. So, you have to take into consideration the Tg as a major factor when choosing the right epoxy for your given application.
All these key epoxy differences, as well as the different types and brands, are important to know. This knowhow helps to prevent an IoT device undergoing PCB microelectronics assembly from being subjected to failure at the outset.
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