- Sample prep
There are two common types of epoxy packages: thermoset epoxy used for PDIPs and the like, and epoxy resins used for PGAs. The former are typically dark brown or black and mixed with glass beads, while the latter are typically green, yellow, or brown with layered fiberglass. [Thermoplastics for Packaging 1]
Unlike plastics, once an epoxy is set it cannot be melted. However, there exists a temperature at which an epoxy is considerably weakened. Literature may call this “Tg”. This can be exploited to thermomechanically decap packages without chemicals.
Transitions for various epoxies [Smithers Rapra 18, 19]:
|Epoxy resin||Curing agent||Tg (C)|
An epoxy molding compound (EMC) based package is thermoset (cured) by transferring it hot into a mold and then quickly (a few minutes) set by keeping at an elevated temperature. I think its for this reason that they are often referred to as “mold compound”. Also these are often called “plastic” packages but as far as I can tell this is a misnomer (example: a plastic dual inline package (PDIP) is really epoxy/glass). [Thermoplastics for Packaging 77] mentions that some early packages in the 70's used thermoplastics. More than likely the term was carried over even though it no longer strictly applies (likes MOSFETs with poly gates…).
XXX: Dynaloy decap is aginast tetramine, Tg also leans towards TETA
First a die is attached to a leadframe with some polymer adhesive. (XXX: what holds the leadframe together?) This is heated for quick cure and then bond wires are attached. The chip is now ready for encapsulation and are placed in rows in a heated transfer mold. Chips are seperated by a “series of runners and gates. EMC in the form of solid pre-heated preform (called a puck), is moved into the chamber and heated to melting. An auxiliary ram then pushes the liquefied material through the runner and gates into the cavities, completing the transfer process and encapsulating the chip and lead frame. Post heating may be required to fully-polymerize the epoxy.” [Thermoplastics for Packaging 4]
Setup time is around 30 seconds. For example [PCN0702]:
|Epoxy||Temp (C)||Gel time (s)|
|Sumitomo G700||175||30 seconds|
Many thermoset epoxies contain bromine for flame retardation [Thermoplastics for Packaging 3].
The following have been observed:
This is temporary staging, will eventually be moved to the Archive. NOTE: these results are biased around MP8000CH4 since I used it to find the others
Sample Tg [PCN0702]:
[Hitachi EMCs] lists more Tg in about the same range
[SI chapter 3] shows “BT Resin Glass Epoxy” as the substrate for “OMPAC Ball Grid Array From Motorola”
|Solid epoxy resin||N/A||2-20|
|Carbon Black||1333-86-4||< 1|
|Crystalline Silica||14808-60-7||< 5|
|Brominated epoxy resin||68541-56-0||1.6-3.5|
|Brominated epoxy resin||68541-56-0||1|
|Epoxy, cresol novolac||29690-82-2||5-15|
|Brominated epoxy resin||68541-56-0||1-3|
Epoxy is Poly[(o-cresyl glycidyl ether)-co-formaldehyde]
Used to make packages very similar to FR4. Occasionally used to make certain optical packages, although typically these are plastic. Above: typical epoxy resin package.
BT resin seems common. TODO: others
Packages commonly use epoxy or silicone. “The last of the three basic encapsulants is polyimide. Polyimides are used less often in IC packaging as an encapsulant. They are fairly common in die-attach adhesive formulations.” One of the charts also mentions BCB (?). [Materials and methods for IC package assembly]
Things to look into: