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Method for high-density wire bumping

IP.com Disclosure Number: IPCOM000101574D
Publication Date: 2005-Mar-16
Document File: 4 page(s) / 124K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for high-density wire bumping. Benefits include improved functionality, improved performance, improved reliability, improved ease of manufacturing, and improved cost effectiveness.

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Method for high-density wire bumping

Disclosed is a method for high-density wire bumping. Benefits include improved functionality, improved performance, improved reliability, improved ease of manufacturing, and improved cost effectiveness.

Background

      High-density wire bumping and smaller bump size is required as form factors decrease in size. If new equipment is required, a large capital investment is required to replace deposition and sputtering process equipment (see Figure 1).

              Conventionally, a controlled collapse chip collect (C4) eutectic Sn-Pb solder bump is produced using a low-end paste printing process as the back-end process of wafer fabrication. The paste printing process has a limitation to the higher density and smaller pitch size, particularly when the bump sizes less then 100 mm due to the difficulty of visual alignment.

      Voiding and failure can occur from the presence of a phosphate layer on top of the C4 solder bump surface.

      The conventional C4 solder bump process can be implemented using the following steps:

1.   After base layer metallization (BLM), develop.
2.           Perform a dry-film process to develop the cavities for paste printing.
3.           Perform paste printing (a series of lithographic processes).
4.           Reflow the solder.
5.           Perform dry-film stripping.
6.           Reflow the solder for solder-sphere forming.

      Solder paste printing technology has a limitation at ~75 mm of solder bump diameter. Solder paste printing faces a problem of forming high standoffs due to the limitations of paste release, paste smearing, and forming uniform height.

      Wire bonding processes conventionally provide a stable and capable technology for forming the electrical interconnection of a component package. Wire bonding has a proven higher alignment capability and the capability to produce smaller bumps sizes. Wire bonding is clean-room compatible due to eliminating the dusts generated by the paste printing process. As a result, clean-room maintenance cost is reduced.

      Conventionally, bump redistribution is applied to achieve higher density.

General description

      The disclosed method is high-density solder bumping using a wire-bonding process. It uses a standard BLM on a component silicon die surface. After reflow, the interconnection is established and C4 solder bumps are formed. The method replaces the dry-film process step and paste printing process. The method can be extended to any form of solder and wire composition.

              The key elements of the disclosed method include:

•             Wire-bond technology that forms eutectic Sn-Pb solder bumps on a silicon die surface

•             Bumps that range from 53 mm to 33 mm diameter

•             Standard BLM layer that forms good bonding with eutectic Sn-Pb solder wire during the stud bumping process

•             Reflow on the eutectic Sn-Pb stud bump that forms C4 bumps without the dry film

•            ...