Why is it important to protect bare dies after wire bonding especially when your product is undergoing PCB microelectronics assembly?
The answer comes in two parts. One, you need to protect the die for mechanical sturdiness. Two, moisture can at times creep in to create corrosion or oxidation surface finish. Therefore, both the die and associated wire bonding need to be protected.
Consider that PCB microelectronics assembly involves very delicate, very fine wire, usually gold. Typical wire gauge is one, two three, and five mil. Five mil wire is typically used for very high current applications. Most often, wire gauge used is one mil. But in some cases, sub mil, like 7/10 of a mil is also used when the die pitch is too tight.
There is more to learn about this subject and you can read about it in our SMT007 column.
In the meantime, here are some tips and hints to get you started.
- Both the die and the wire bonding, itself, must be protected from assembly processes including handling, testing, and fixturing.
- There are two distinct sealing compounds for protecting the die and wire bonding – epoxy glob top, Fig. 1 with an auxiliary one called dam and fill and the second type is lid and cover.
- Glob top epoxy material characteristics include non-electrically conductive, thermally conductive, low coefficient of thermal expansion (CTE), and good adhesion.
- You want assurances that the low CTE allows the epoxy material to expand and contract on a very small percentage in very low numbers.
- The lid and cover method can be a ceramic, plastic, or glass lid, depending on customer specifications and application.
- Glob top is more widely used than lid and cover. Lid and cover has to be made for a specific application and has to be cured at a certain temperature.
Protecting bare dies on a PCB or substrate is one of the major processes of microelectronics assembly. Microelectronics assembly and manufacturing work together with traditional SMT manufacturing for complete PCB hybrid manufacturing of today’s smaller form factor products, including IoT, wearables, and portable devices.