As IoT devices gain greater acceptance within mission critical industries such as industrial, medical and aerospace, product integrity and reliability are of the highest order. Bare chip or die protection is at the top of the list for ensuring IoT reliability and product integrity.
IoT devices — in most instances — are based on factors requiring a combination of conventional surface mount printed circuit boards (PCB) and microelectronics manufacturing, which creates hybrid manufacturing. IoT device PCB microelectronics manufacturing most often requires dies to be placed on a PCB, which can range from rigid, flex or a combination of rigid-flex circuits. In some cases, dies can also be placed on a substrate.
Why protecting die and wire bonding is important
Protecting a bare die and its associated wire bonds is critical to assure mechanical sturdiness and avoid moisture, thus maintaining a high degree of reliability for the IoT user. PCB microelectronics assembly requires a very delicate, fine wire that is generally made with gold. The typical wire gauge ranges from one, two, three and five mil. Five mil wire is typically used for very high current applications. More often than not, one mil wire gauge is used, but in some cases, sub mil — 7/10 of a mil — is also used.
It’s highly advantageous for IoT device OEMs to get a good handle on how best to protect bare dies and their associated wire bonding. That way, OEMs can assure themselves of high levels of product reliability.
Methods to protect die and wire bonding
There are two distinct sealing compound methodologies for protecting the die and wire bonding. One is called by the unusual name of glob top, which actually fits very well since a glob of epoxy is placed on top of the die to protect it.
Dam and fill is a similar die sealer, which is in this same glob top category. It involves creating a dam or wall around the die and associated wire bonding by using a high viscosity material. Then, the middle or cavity surrounded by the dam is filled with a low viscosity epoxy. Thus, the high and low viscosity materials act as an effective protector of the die and wire bonding.
Lid and cover is the second encapsulating protected method. It can be a ceramic, plastic or glass lid depending on customer specifications and application. Such a lid can be soldered onto the substrate if the material is aluminum, nickel, gold or hot air solder leveling.
In some cases, a specialized lid with B-staged epoxy is provided. Most likely, it is custom made with epoxy already applied on the lid or cover. All that is needed in this case is to cure it and then apply it around the die and wire bonds. While the lid and cover protection method isn’t as widespread as glob top, the lid and cover approach is used depending on specialized PCB applications.
Reliability not only depends on the right bare die sealing compound for the right IoT PCB application, but also the level of microelectronics manufacturing experience. PCB microelectronics manufacturing personnel must have a good understanding of these protection methodologies and how to accurately apply them to form a perfect microelectronics assembly.
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