“As long as people have been in the business of inventing, others have been in the business of faking their inventions”
The success of our global economy relies on the free flow of information and products across multiple geographical boundaries. In a networked society, markets transcend political borders to reach every corner of the globe. With such connectivity come serious challenges to protect the homeland from foreign and domestic threats. The influx of counterfeit electronic components in our supply chain is an ever-increasing threat to our economy. The latest report issued by the US Department of Commerce states that the number of counterfeit incidents almost tripled between 2005 and 2008.
Radiography (or x-ray inspection) is a ubiquitous technique to all recent and upcoming counterfeit detection standards, including IDEA 1010B, CCAP 101, AS5553, AS6081, and AS6171. X-ray inspection gives you the unique ability to “see” what is inside an electronic component without damaging it. To illustrate how x-ray images represent an electronic component, Figure 1a shows a simplified side view diagram of a typical plastic molded part. The top view x-ray of a real plastic molded component is shown in Figure 1b. The dark regions in the x-ray image represent dense areas in the component. Conversely, the light areas represent light areas in the field of view. For this reason the area around the component is represented in white. The x-rays traveling through the different density areas of the component under inspection cast a shadow onto the camera. Thus this x-ray imaging technique is also known as a shadowgram.
A common technique used to identify counterfeit components using x-rays is to utilize an exemplar as a basis of comparison. The exemplar samples can be obtained in different ways. The usual method includes the comparison to components in previous lots that were obtained from trusted suppliers. In the event that such a priori information is not available, you can compare the part to another one currently in use. In this case, it is often necessary to x-ray the printed circuit board with the assembled component. Both options, if available, must be used carefully, as manufacturers can change the leadframe structure, die size, and wire bonding schemes without notice. Therefore, it is imperative for the user to seek more information on the part before judging it a counterfeit suspect.
The major challenge in the determination of a counterfeit component is the usual lack of an exemplar that can be used as a basis of comparison. The most common strategy used in this case to assess the authenticity of an electronic component is to perform the comparison within parts of the same lot, as seen in Figure 2. This in-lot comparison is very powerful because all parts within the lot must be identical. However, often time counterfeiters remark different parts (that do not have identical x-ray images) to fulfill an order. Even if you do have an exemplar available, it is also common to find counterfeit components mixed with good parts. That is the counterfeiters’ attempt to circumvent detection by customers doing tests of just a few parts in the lot. For this reason it is imperative to test all parts to assure homogeneity within a lot. Until not long ago testing thousands of components was cost prohibitive. However, recent breakthroughs in the automation of radiography inspection have made it possible. New systems in the market, like the TruView X-ray inspection systems, have made possible the automated inspection of thousands of parts in trays, tubes, or reels.
What are you looking for?
When looking for counterfeits, the most common things you may find inside the components are:
1) Inconsistent die size – because the die is a thin piece of silicon, a top view x-ray image will likely not show you the die. However, the die attach fillet (see Figure 1) is dense enough to appear in a top view x-ray image. As a result, you can determine the size of the die by measuring the boundaries created by the die attach fillet. Since counterfeiters often remark different parts to pass as the part you are looking to buy, it is almost inevitable they will mix different components with different die sizes. Another technique to verify the size of the die is to take a side view x-ray image of the part. In this case the through density of the die is enough to appear in the x-ray image.
2) Inconsistent leadframe – Similarly to the previous case, counterfeiters often mix parts with different leadframes in the same lot.
3) Broken or missing wire bonds – A broken wire bond may be a result of extreme mechanical or thermal stress applied to the part. Similarly, the absence of wire bonds is the sign of a suspect lot of parts. It is very important to note that some parts are packaged with Aluminum wire bonds. Since Al is a low-density material, these wire bonds will not show in an x-ray image. For this reason, if you cannot see the wire bonds in a part, we recommend decapsulation it to confirm that they are not Al wire bonds. X-ray system can show Gold and Copper wire bonds.
4) Incorrect wire-bonding diagram – Even if the parts have the same leadframe and die size, you must verify that the wire-bonding diagram is consistent.
5) Missing die – Although you may not be able to see the die directly, it is important to verify the presence of wire bonds and the die attach fillet. We found several examples of empty packages being sold as functioning parts.
6) Inconsistent die attach voiding – the mature semiconductor manufacturing process leads to consistent parts. The presence of large variations in the die attach voiding may be a reason to fail the parts.
The following example in Figure 3 shows the x-ray image of a section of a reel of Samsung K6X1008C2D CMOS SRAM with mixed leadframes and die sizes. This is a clear example of a reel where good and bad parts have been mixed together in an attempt to deceive a user doing sample testing of the lot.
Recent developments in the electronics industry and the constant push towards globalization have leveled trade between nations across the world. As a result, worldwide trade has given criminal groups the opportunity to profit by inserting counterfeited goods in the flow of commerce. Although a small fraction of the overall counterfeit enterprise, fake electronics components are extremely dangerous as they enter military, medical, aerospace, and other critical applications. For this reason, in this article we covered radiography as one of the few inspection techniques widely used to identify counterfeit components.