Browse Prior Art Database

Method for flux injection

IP.com Disclosure Number: IPCOM000146412D
Publication Date: 2007-Feb-13
Document File: 4 page(s) / 245K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for flux injection. Benefits include improved functionality, improved performance, improved reliability, improved throughput, and improved cost effectiveness.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Method for flux injection

 

Disclosed is a method for flux injection. Benefits include improved functionality, improved performance, improved reliability, improved throughput, and improved cost effectiveness.

Background

      Conventionally, flux is applied using a printing process that can be implemented using the following steps (see Figure 1):

1.   Place a stencil on a substrate.

2.   Dispense flux onto a stencil.

3.   Force the flux through the stencil openings using squeegee blades.

4.   Apply solder using the same stencil printing process.

5.   Dispense solder paste onto the stencil.

6.   Force the solder paste through the stencil aperture using a squeegee blade.

7.   Place die-side capacitors (DSCs) on the package using a chip shooter.

8.   Release the substrate from the stencil.

      However, the flux printing process is the source of several problems, including the following (see Figure 2):

•     Height of the substrate solder bump above the surface of the stencil, preventing the free application of the flux

•     Carrier warpage

•     Warpage on the reels

•     Squeegee deformations

•     Damage to oversized bumps due to squeegee movement against the substrate

•     Process restrictions due to a requirement for a flat substrate

      Making the stencil thicker can raise the stencil top above the solder bump height. However, excessive flux can cause the die to float and tilt or misalign.

      A spray flux application method has been developed to solve the problems. However, initial results are limited, including the following problems:

•     Nonuniform application of the flux coat over the substrate surface

•     Poor cap adherence

•     Shorting

•     Unstable flux volume application among consecutive carries

General description

      The disclosed method is flux injection. An inverted carrier holds the substrate with the substrate bumps face down and dips it into a flux bath that injects flux.

 

      The key elements of the disclosed method include:

•     Bare substrate with DSCs attached

•     Inverted tray faces substrate bumps down and dip into flux bath

•     Flux bath with flux injection system and air vent in the compartment

      The disclosed method applies flux on substrate bumps, regardless of bump height distribution. The method eliminates the use of squeegees and stencils. Additionally, the method enables DSCs to be attached earlier in the assembly process.

Advantages

    ...