My understanding of flip chip-
     
     A method of direct chip attachment (DCA); IBM may not have developed 
     flip chip (?)but they probably perfected the design and manufacture of 
     flip chip in the late 1960's, on their humongous MCMs, dubbed "Thermal 
     Conduction Modules" (TCM) by IBMer's. A cutaway drawing of an IBM TCM 
     was the cover art on a late 60's or early 70's issue of Scientific 
     American. 

IBM called their flip chip "C4", which I think stands for "controlled collapse 
chip connection". C4 mounts the unpackaged die face down, via the reflowable C4 
balls. Each ball sits on numerous metallization layers which have been deposited
at each chip I/O pad. The metallizations, their size and shape, the size of the 
opening in the chip passivation around each C4 ball, ball metallurgy, and the 
surface tension of the reflowed balls---all these lead to the controlled 
collapse of the balls into a specific geometric form on the MCM substrate.

Flip chip requires the application of an "underfill" compound, which surrounds 
the reflowed balls after substrate attachment; I think this is done to provide 
reliable attachment under thermally induced cyclic loads.

Flip chip is obviously the grand-daddy of BGA, wherein the ball diameters and 
pitch are smaller for flip chip, as compared to BGA.
Hope this helps.

Michael Alderete
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______________________________ Reply Separator _________________________________
Subject: what is a flip chip?
Author:  [log in to unmask] at _internetcc
Date:    4/9/97 10:23 AM


Everyone -
     
What is a "flip chip"? I work in the PCB fabrication industry and see 
this term a lot in magazine articles. I've never heard the basic 
definition. Please help me increase my knowledge base.
     
Thanks
     
     
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