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Package-to-Package Stacked Next Generation Multiple SCSPs with Flat Ribbon Second-Level Interconnect

IP.com Disclosure Number: IPCOM000126995D
Publication Date: 2005-Aug-16
Document File: 4 page(s) / 394K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for an SCSP that uses a substrate with built-up layers of peripheral lead fingers around the devices stacked in the package. With the device bond fingers and the lead fingers at the same height, the second-level interconnect (SLI) between the devices and the substrate are completed via flat ribbon-type wires. Benefits include reduced package thickness, reduced process costs, and higher assembly yields.

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Package-to-Package Stacked Next Generation Multiple SCSPs with Flat Ribbon Second-Level Interconnect

Disclosed is a method for an SCSP that uses a substrate with built-up layers of peripheral lead fingers around the devices stacked in the package. With the device bond fingers and the lead fingers at the same height, the second-level interconnect (SLI) between the devices and the substrate are completed via flat ribbon-type wires. Benefits include reduced package thickness, reduced process costs, and higher assembly yields.

   

Background

Currently, there are issues associated with stacking multiple devices in mixed-technology SCSPs, especially devices with similar or identical sizes. It is difficult to accommodate the static device bond pad layout within the interconnect process. It is also difficult to stack multiple mixed-technology SCSP packages.

Conventional SCSPs use spacers to offset the upper devices in the z-direction, allowing the lower devices to be wire bonded to the substrate. In some instances, redistribution layers (RDLs) are required to reroute device bond pad locations to a different pattern that is more suited to device stacking and wire bonding. Using flexible polyimide substrates, package stacking can also be accomplished with a conventional SCSP as a top package stacked on a folded flex bottom package. Traces from the top package are routed through the bottom package traces that run through the fold flap (see Figure 1).

General Description

For package assembly, the disclosed method uses current processes and tools to manufacture SCSPs, except for the interconnect process for the ribbon SLI.  In its simplest form, one end of the conductive trace contacts the device bond pads and the other end to the substrate lead fingers; the conductive traces are secured to the bond pad and lead finger with a conductive adhesive, and then released from the pattern carrier. This process can be developed as a modified TAB- or lead-bonding process. The die attach adhesive between devices acts as an insulator, and prevents device-to-interconnect shorting.

Since the device-to-substrate interconnect is limited to two dimensions instead of three, the complexity of the interconnect process is reduced considerably. The ribbon SLI is pattern transferred in parallel. Manufactured to accommodate the dimensional tolerances of device bond pads and substrate lead fingers, the two-dimensional pattern can be transferred by a flexible film type carrier as long as the ends of the conductive traces are aligned with the appropriate bond pads and lead fingers. The level of parallelism is determined by the device, substrate, and ribbon SLI manufacturing and package assembly tolerances.

Figure 2a shows the basic...