Nothing special in all of my life.
I am just a nobody and asshole as well.
However, I did invent a patent in my expertise.
This patent was highly related to assembly process in semiconductor field.
In 2008, most of the smartphones used AP (Application Processor) + DRAM chips
on PCBs (Printed Circuit Board).
Someone invented an advanced package which includes AP and DRAM in it.
In the very early phase, Assembly house put AP and DRAM side-by-side and
connected them together by wire-bonding process.
This innnovated package structure was fine in workability by 2009 'coz
wire-bond tech was capable of meeting the speed requirement of smartphones.
Nevertheless, the speed and AP and DRAM was getting faster and faster.
Many tech. guys thought the wire-bonding tech could be out-of-date soon in
some point.
Another creative package structure came out to try to connect AP and DRAM
by shorter paths. This package was so called "PoP" - Package-on-Package.
PoP consisted of 2 major packages - one was the package of AP and surely the other
one was the package of DRAM. Totally different from the previous structure,
PoP connected these 2 packages in vertical direction; not side-by-side anymore.
In the very beginning, only 200~300 connection pins between AP and DRAM was
enough since the I/O pin counts were still limited. But many people from tech.
industry also thought about this issue how to make more and more I/O pins to
satisfy more sophisticatedly new-generationed smartphone. Thus fine-pitch of
PoP would be a necessity to meet the request of higher I/O pin-count.
That's why I was asked to find the tiny-sized copper ball because my boss would like use them
to be the conductive connections between AP pakcage and DRAM package.
This idea was pretty much good, however, the most problem of this method was
the shape of copper balls. No one had the ability to put DRAM package on
the sepherical copper balls and utilized reflow process to form the good
connections. As you guys might know, reflow needed strong wind to transit heat.
This sort of wind might make the severe shift of top DRAM package in reflow.
Therefore, I thought a way to encapuslate all copper balls in molding compound
and revealled them afterwards by cutting the molding. After this cutting, the
top shape of copper balls would become flat and we could put top DRAM package
on it withouth any concern in reflow furnace...
(To be continued...)