Fujitsu Microelectronics has developed an ultra-high density, multi-chip package (MCP) that can support up to eight chips. This development was made possible by the company’s advances in thin chip processing and multi-stacked package technology.

Thin chip processing is a special wafer-support technology that permits chips to be polished down to a thickness of only 0.025 mm and multi-stacked package is a technology which enables the stacking of boards mounted with chips using lead-free solder balls. This package is functionally equivalent to a single package.

The new technology provides the smaller, thinner, more densely integrated and higher-capacity LSI packages, such as chip-scale packages (CSPs) and MCPs, demanded by today’s mobile phones, digital audio/video equipment, IC Cards and compact hard disk drives.

Typically, the mounted surface area on a circuit board allows for 1.2-1.6 mm thick packages. The thickness allowed for one chip depends on the number of stacked chips per package. Thus, three-stacked packages require 0.15 mm thickness per chip, while four-stacked need 0.1 mm, and five or more demand 0.08 mm or less. To create chips less than 0.1 mm thick, however,
requires a chemical process beyond conventional polishing techniques, entailing longer chip processing times, higher equipment costs and problems associated with environmental emissions.

The new MCP is the result of improvements in both ultra-thin wafer processing and advanced multiple chip packaging technology. This slimming process enables the production of wafers as thin as 0.025 mm without the use of chemicals, resulting in reduced manufacturing cycles, equipment costs and impact on the environment.

While Fujitsu’s existing MCPs could house a maximum of four chips within a 1.6 mm package height, the new wafer-slimming process alone makes it possible to produce MCPs with up to six-stacked chips. Combined with the company’s advanced new packaging technology, a maximum of eight chips (package height of 2.0 mm) can now be mounted onto a single MCP. Another benefit of these technological advances is that IC Cards and compact hard disk drives, which
previously could hold only two-chip packages, are now able to support three-chip combinations.

The new packaging technology is an ideal mounting technique for ultra-high density packages. Until now, each circuit board was limited in the size of chip that could be mounted onto it, and complications arose in configuring outside electrical connections when layering chips of identical sizes, as electrical connectors could not be stacked to reach upper layers. With this advanced packaging technique, chips are attached to one or both sides of the circuit board while using lead-free solder balls to bond packages to the board. This makes it possible to stack a number of chips of all shapes and sizes.