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Removal of Inclusions in Solder Joints by Induction Force Using Electromagnetic Fields

IP.com Disclosure Number: IPCOM000100652D
Publication Date: 2005-Mar-16
Document File: 4 page(s) / 24K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a device that applies a constant electric current and magnetic field across solder bumps. The disclosed method removes inclusions from the solder bumps and ensures that the eutectic and single-phase solder alloys remain clean.

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Removal of Inclusions in Solder Joints by Induction Force Using Electromagnetic Fields

Disclosed is a method for a device that applies a constant electric current and magnetic field across solder bumps. The disclosed method removes inclusions from the solder bumps and ensures that the eutectic and single-phase solder alloys remain clean.

Background

In the current no underfill flow (NUF) process, underfill particles can become trapped inside solder joints during the collapse of the flipped chip (see Figures 1 and 2). In NUF, the chip attach and underfill dispense processes are performed in a single step; underfill material is already in place during the chip attach process. During NUF, underfill particles must be removed or prevented from being trapped to allow the formation of a good connection.

Current solutions modify the shape of the substrate and die bumps, which displace the underfill material already in place during the chip collapse. This solution is being tested, but it has not provided a complete solution to the problem.

General Description

The disclosed method uses a direct current and a magnetic field, both constant, to remove any particle from the joint inside the solder bump. A particle inside a conductive media (i.e. solder alloy) disrupts the flow of the electric current, which interacts with the magnetic field (see
Figure 3). The particle does not need to be conductive to disrupt the current distribution. Any particle with a different conductivity than that of the solder disrupts the electric current distribution. When the electric current and magnetic fields are constant and direct (i.e. not alternating), the trapped particle is forced perpendicular to the plane containing the directions of the electric and magnetic fields. The disclosed method removes the trapped particles in the following sequence:

1.      The chip is attached to substrate....