Apart from analyzing integrated circuits and Printed Circuit Boards (PCBs) for detecting the causes of a failure, we also sometimes need to find out the exact composition and mechanics of “healthy” ones. This is because such electronic components are subject to a number of regulations before being allowed into the marketplace including hazardous substance regulations. Depending on where the chips are going to be shipped to, these may vary greatly.
For example, the EU has Directive 2002/95/EC dealing with the restriction of six types of substances which can be present in electronic components placed on the market. In the United States, there are fewer such restrictions and California is the only state so far which has them in place, and they are in turn based on the same EU directive. In this article, we take a look at some specific restrictions as well as the methods we use to determine whether or not the chips are compliant.
Overview of the RoHS directive
This directive is commonly called the “lead-free” directive, probably because people are most familiar with lead as a dangerous substance, but there are five other compounds and elements which need to be looked for namely Mercury, Cadmium, Polybrominated Diphenyl Ether (PBDE), Hexavalent Chromium and Polybrominated biphenyls (PBB). It may not be possible to rid the chips entirely of these substances, but the concentrations must never exceed 0.1%. This translates into 1000 parts per million (ppm.) Cadmium is even more toxic than the rest and cannot be over 0.01%.
An important point to note is that these concentrations refer to any part which can be physically removed. Meaning that the weight of the rest of the system is irrelevant while computing the concentrations.
Detection of trace prohibited elements
It’s clear that we need two types of tests in order to certify compliance with RoHS directives. The first test lets us know if the restricted substances are present in the first place. The second tells us the exact quantities to determine whether or not they’re below the limits prescribed.
Emission spectroscopy is typically used for both these purposes. As we saw earlier, deep level transient spectroscopy has a remarkably high sensitivity and can detect one in 10^12 parts! Auger electron spectroscopy can also be used for this purpose.
The procedures are slightly different from regular failure analysis of course right from the initial stages. There’s no detective work involved here. But they’re absolutely essential if you need to market your chips in the EU and even in the US where laws relating to dangerous substances are being put in place even as you read this.