What is the black stuff on the PCB boards??? Glob Top or Black Blob
Have you ever observed a black rock-solid substance on the PCB boards ??? If yes, do you know what actually it is and why it is placed there ??? To clarify all your doubts continue reading this article.
The original name for this black rock solid material is Glob Top, in general, we also call it as a Black Blob.
What is this Glob Top?
Glob Top is an encapsulation material used to cover the wire bonds of the sensitive semiconductors which can be broken easily. Generally, these are applied to the PCB boards where the fragile semiconductors are placed. This made from Epoxy Resins.
In normal usage, the terminology of calling this Glob Top has changed to Black Blob (which means a black thick viscous liquid).
Why we use this Glob Tops?
This glob tops will help the semiconductor to work for a long lifetime that too in harsh conditions. This can also resist the heat capacity of around 85 ͦ C for about 2000 hours without any damage to the semiconductor.
Not only this, it also noted that using this Glob Top is economical to the manufacturer.
Types of Glob Tops :
There are two types of Glob Tops, which are segregated according to their application methods and the materials used in making the glob tops.
- Single material hemispherical Glob Top :
The single material glob top uses a thixotropic material to form a dome of protection on a semiconductor and wire bonds
2. Two material dam-and-fill Glob Top :
A dam-and-fill glob top utilizes two materials, in a two-step process. Initially, a thixotropic epoxy dam is formed around the area and later a low viscosity epoxy fills the cavity.
Here the two methods don’t show any difference in terms of protection, but the dam-and-fill protection is used mainly for optical transmission applications.
COB Technology :
This is also detailed as Chip On Board Technology. The entire process of making a Slot on PCB with the semiconductor and covering it with Glob Top is called Chip On Board technology.
Here first the PCB board is selected and the semiconductor is placed on the board, then the wire bonds are given with the utmost care, then next the Semiconductor part along with wire bonds are covered with heated epoxy resins. Later it is cooled and sent for checking purpose.
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