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Method for flux dispensing for solder interconnection assembly

IP.com Disclosure Number: IPCOM000144784D
Publication Date: 2007-Jan-06
Document File: 5 page(s) / 294K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for flux dispensing for solder interconnection assembly. Benefits include improved functionality, improved performance, improved reliability, improved throughput, improved process simplification, and improved cost effectiveness.

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Method for flux dispensing for solder interconnection assembly

Disclosed is a method for flux dispensing for solder interconnection assembly. Benefits include improved functionality, improved performance, improved reliability, improved throughput, improved process simplification, and improved cost effectiveness.

Background

      Flux materials are conventionally applied in the semiconductor packaging industry to remove the oxide layer on the solder surfaces to ensure good interconnection. For example, flux is applied during chip attachment to remove the oxide layer on the substrate and the die bumps to ensure good solder interconnections are formed. However, the fluxing and defluxing processes have several issues, including the following:

•     For ultra-thin die and stacked die packages, die-to-underfill or underfill-to-solder resist delamination, especially under stress conditions, due to flux residue after defluxing

•     For stacked chip scale packages (SCSPs), weak adhesion between gold wire and pad or the nonstick on lead (NSOL) issue due to contamination of wire bond pads (lead frames) by flux residue

•     Distorted substrate bumps due to flux stencil printing

•     Die misalignment due to excessive flux volume

•     Solder voids due to bump nonwetting because of insufficient flux volume

•     Multiple processing steps for conventional flux stencil printing, including the following (see Figure 1):

      1.   Align and place the stencil with the substrate bumps and pads.

      2.   Knead and load the flux, and place the stencil for printing to the substrate.

      3.   Align and move the squeegees horizontally.
4.   Remove the substrate after printing.

      5.   Perform die pick-and placement, the chip-attach process, and the deflux process.

      Excessive flux residue is conventionally reduced by optimizing the deflux process through module characterization. However, this approach is not a full-proof solution and requires extensive resources a characterization effort that is expensive.

      Flux spraying is the conventional solution to eliminate the distorted substrate bumps.

General description

      The disclosed method is flux dispensing for solder interconnection assembly. The method uses a specially designed tool to dispense a predefined amount of flux from the flux syringe onto designated substrate bumps. The pressurized dispensing system enables efficient and low-pressure defluxing for ultra thin and stacked CSPs. The controlled dispense volume ensures sufficient flux volume is dispensed, reducing excessive/insufficient flux coverage on the substrate bump-pad.

      The key elements of the disclosed method include:

•     Flux dispensing tool with fluxing tips that are identical to the substrate b...