Application Notes

BGA Cross Section Analysis

Background

The packaging of electronic components on printed circuit boards (PCBs) has become denser due to the demand to make mobile electronic devices that are smaller and faster with increased functionality. Packaging methods for IC parts, in particular, have been shifting to bare chip packaging where IC chips are packaged directly on PCBs. The IC chips are mounted on the surface alongside the packaged electronic components (e.g., QFP and SOP). This manufacturing shift has caused PCB density to increase significantly. There are several methods in bare chip packaging to connect chips’ electrodes to PCBs. Flip chip packaging is an optimal method for achieving high package densities. Specifically, bumps formed on the chips are directly connected to the boards. A typical technique for the analysis of the interfaces of bumps and IC chips to be mounted, is to cut the mounted chips in order to observe the cross section of the bumps. The cross sections are polished to visualize the minute projections and depressions that remained on the surface. The challenge is to observe differences between the raw materials forming the bumps and the areas around the bumps while maintaining the entire visual field in focus. Often electron microscopy is used because most optical microscopes are not up to the challenge.

Olympus solution

The Olympus Digital Microscope DSX with EFI function, allows the operator to capture images in which the whole visual field is in focus. This is achieved by shifting the focus at high speed and by taking multiple images. The DSX approach allows the operator to take clear color images of samples with minute projections and depressions on the surfaces without using an electron microscope.