<<Can anybody actually explain what "organic laminate substrates" are and what the big advantage for LSI is?
The article also mentioned the use of copper:
"Copper is used for signal distribution in the package because of its lower in resistance than the interconnect metallization used in ceramic packages."
Is this similar to the IBM breakthrough on using copper or am I way of base here?>>
RFF, I couldn't find the original article you refer to here, so I am not sure if the link to the article on flip chips provided by E. Graphs is really the answer to your question. If I am off base here, I apologize, but I thought I'd add my two cents worth.
I believe "organic laminate substrates" refers the substrates which are used in BGA (ball grid array) packages. The substrates are made by weaving together a layer of small glass fibers (FR4, for example), and the chips are then mounted on the substrates. One the other side of the substrate are a grid of tiny solder balls which make connections from the package to the printed ciruit board. The connections between the chip and the solder balls are made by routing copper traces across the "organic laminate substrate". As you mention, copper is used because of its high conductivity. However, this is nothing new. Plastic encapsulated QFP (quad flat pack) packages have been using copper traces for years. These are standard in the industry. Ceramic packages, such as Intel uses for their microprocessors, typically use gold routing in the package instead of copper. This is because of higher reliability, but I am not sure of the technical reason. Flip chips route signals directly to the printed circuit board through solder balls attached directly to the face of the chip; there is no need for copper or gold traces in the flip-chip package. This is a major advantage, although I do not buy all the saving glories of flip-chip technology touted in the article. It has its own set of problems.
Using copper for the interconnects within the chip, as touted by IBM, is a whole different ballgame. Historically, aluminum has been used for these interconnects, even though it has a lower conductivity than copper. The main reason for this is that copper causes serious problems when it comes into contact with silicon. When chips only used one layer of metallization, which directly contacted the silicon, using copper was not realistic. Now, with multiple layers of metallization and the use of tungsten plugs to connect between layers, copper can be used without coming into direct contact with the silicon. The main obstacle now is the fact that the whole infrastructure of the industry is geared toward using aluminum metallization. Moving to copper metallization increases the speed at which your chips can run, but it also means designing a new manufacturing process, which is not easy or cheap.
I hope I shed some light on this without getting too much off topic.
G.P. |
