23.09.2021
Encapsulation innovation: IDEALmoldTM 3Ge, Image source: ASMPT
Encapsulation
In simple terms, encapsulation refers to the process of enclosing plastic material around an object, so that a protection volume forms around the object like a capsule. This method has already been in use since the invention of integrated microelectronics (‘Integrated Circuits’ (ICs)) in the back-end semiconductor packaging and assembly process around 40 years ago.
There are many forms of encapsulation such as injection, glob topping, compression and transfer. The purpose of transfer encapsulation is to protect IC assemblies and their interconnections against mechanical interference and hostile environments when in use. This transfer moulding technology might seem ‘ancient’ in comparison to others, but it has made great progress thanks to advances in Plastic Encapsulated Microelectronics (PEM) packages, encapsulation techniques, and even the plastic material used to protect ICs.
Understanding Transfer Molding
Transfer molding is an encapsulation method where a thermoset plastic material known as ‘epoxy’ is loaded in pellet form and preheated inside a metal pot, then forced to flow into the mould cavities where the PEM in question to be protected is. This process uses a heated plunger, via a plumbing system utilizing a series of gate and runners (see Figure 1).
Figure 1: Complete Transfer Molding Process, Image source: ASMPT
The advantages of transfer moulding are that it facilitates standardization, with less variation in package thickness. This is because it holds tighter tolerances for parts that are more intricate to form. This in turn generates a higher Unit-Per-Hour (UPH) for high cavity count applications. This means shortening the production cycle, a faster setup time, and finally lower operating costs. In addition, transfer molding tooling is cost efficient when moulding a large number of PEMs within a typical 30-second machine cycle time.
Figure 2: Advances in Transfer Moulding - PGS Technique. Image source: ASMPT
One key technical advantage of transfer moulding is its Pinnacle Gating System (PGS). The PGS uses pin gates (see Fig. 2), which are ideal when a packaging designer needs to maximize a substrate’s size that produces a high quantity PEM. For example, when mould flow induced stresses must be properly controlled, specifically by minimizing flow jetting in order to reduce stress to the wire bond to minimize ‘wire sweeping’ (Fig 3.)
Figure 3: Wire sweeping. Image source: ASMPT
The PGS technique is also cost-efficient as it optimizes the available space in a lead frame or substrate, resulting in a high UPH output due to minimal wastage of usable space. It also reduces epoxy wastage (which is eco-friendly) and provides an operational gain via lowered cost-per-unit.
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