Casio MR-80 Radio
World ACAF Premiere
Assembled
Disassembled
First Use of Anisotropic Conductive Adhesive Film for Flip Chip Assembly on an Organic Substrate
Prismark went shopping in Japan again! This time it is a radio from Casio. Why read a bulletin on a radio? This is the first system to use anisotropic conductive adhesive for flip chip assembly to an organic substrate. Read on!
The Casio MR-80 is an AM/FM radio that is used to receive certain radio stations in Japan that broadcast audio programs as well as messages. These messages are displayed on the Casio’s integral LCD screen. This radio was selling for about $240 in Akihabara, Tokyo, Japan, last month.
The radio was designed to be about the same size as a credit card, only thicker. To meet these specifications, Casio adapted its experience with flip chip-on-glass for LCD drivers to a printed circuit board assembly.
The Casio radio contains three printed circuit boards. Of primary interest is the flip chip board or multichip module, a photo-via built-up multilayer board with five flip chip die as well as numerous packaged components. The flip chip die include extensive test patterns for a built-in self test (BIST) at wafer level, and the die pads are electroplated with gold.
An anisotropic conductive adhesive film is placed onto the substrate. Casio temporarily mounts the die and performs a functional test based on a test pattern stored in ROM. If the test is negative, the faulty die and the conductive adhesive film are peeled off and replaced. Only once the test is positive is the anisotropic conductive adhesive film cured through pressure and heat.
Anisotropic conductive adhesive film has long been used for chip-on-glass in LCD driver applications: A bare driver IC is mounted onto the LCD glass panel as a flip chip, whereby a conductive adhesive film (or paste) provides the connection between the die’s gold bumps and the ITO traces on the LCD glass. This application requires an adhesive-based connection, because the temperature sensitivity of the LCD makes soldering impossible. Due to the superior planarity of the glass, and the CTE match between the glass and the silicon die, such connections achieve high yields and high reliability. Organic substrates, on the other hand, are neither planar nor do they match the CTE of the silicon.
Isotropic conductive adhesive paste has been used to attach stud bump flip chip to organic substrates, for example in a Fujitsu Pentium built-up multilayer MCM-L now shipping in their sub-notebooks (see upcoming Prismark Bulletin). Such constructions also utilize an underfill to provide stress relief caused by the CTE mismatch. Casio’s approach, on the other hand, combines the function of the conductive adhesive and that of the underfill in a single material, thus greatly simplifying assembly.
We have no complete data yet on reliability, but if flip chip anisotropic conductive adhesive assembly and built-up multilayer technology can be had for a couple of hundred dollars, are other applications far behind?
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Copyright
© 2000 [IEEC]. All rights reserved. Revised: February 28, 2002 .