Silver(Ag) is easily corroded by sulfur compound gas*, etc. Therefore, IC parts are packaged so that the Ag-plated portion is not exposed to the outside of the package.
If Ag plated portion of the lead frame is exposed to the outside of the packaging resin, Ag corrodes and Ag causes ion migration (in the case where there is a potential difference between terminals), resulting in a short circuit between terminals. In the environment with a higher humidity, corrosion can be accelerated.
*Trace amount of sulfur compound gas may be present depending on the region and operating environment.
* Interface between chip and the packaging resin interface
The failure occurred on the LSI product after mounting on the printed circuit board.
As a result of checking for interfacial peeling between the chip and the resin using the scanning acoustic microscope/tomograph (SAM/SAT), a peeling was found at the chip and the packaging resin interface .
It is presumed that since the packaging resin had absorbed moisture, a steam explosion occurred due to the sudden heating during reflow, leading to a break of the wire.
The figures below show a case study in which operation caused unstable behavior in a certain electronic board, and the related IC component was investigated to clarify the cause.
The graph at the left shows the results of measurements of the electrical characteristics of several terminal pins, which revealed that 1 pin was open. Based on this, it was estimated that an abnormality had occurred in the wiring or connection of 1 pin.
The mold resin of the IC product was dissolved, and the chip surface was observed. The result is shown in the photo at the right. Discoloration of the aluminum wiring of 1 pin in the IC chip can be observed in the part enclosed in the red circle.
It is known that aluminum wiring (Al wiring) generally displays this kind of appearance when it is oxidized or undergoes hydration as a result of corrosion. Thus, it can be understood that malfunction occurred as a result of progressively higher resistance of the aluminum wiring due to corrosion.
Left: Results of measurement of electrical characteristics, right: observation of chip surface
The story of course does not end there. Since the early 1980s, the pace of innovation in semiconductor technology has accelerated. Chips currently in production contain in excess of 1,000,000 transistors. Dynamic random access memory chips (DRAMS), which have set the pace of progress in the industry, have provided a fourfold increase in capacity every three years—even though each increase has required engineers and scientists to solve ever more complex problems, driving the technology to even greater heights.
The photolithographic process used to fabricate the vast majority of semiconductor chips is conceptually relatively simple. The manufacturer applies a layer of photoresist (a material that reacts to light and resists the action of certain chemical agents) to a wafer of material called a substrate. The photoresist is exposed with a predetermined pattern. After being "developed," portions of the photoresist are washed away, leaving the substrate exposed. The substrate is then treated with a chemical agent that may etch material away from the exposed part, deposit material on it, or permeate into it. The manufacturer removes the photoresist and then repeats the process for each of the multiple layers required to form the device.5
The photolithographic process just described has many applications beyond semiconductor chips. The substrate does not have to be silicon (or any semiconductor for that matter), and the product does not have to be electronic circuitry. Manufacturers can use photolithography with masks on a variety of substrate materials, such as glass, polycrystalline silicon, sapphire, ceramic material, superconducting material, magnetic domain material—the list goes on and on, and continues to grow.
Moreover, the resulting product does not have to be a "chip." It can be a flat-panel display, a miniature motor and gears, a thin-film recording head, or any one of a number of items that are not usually considered to be electronic circuitry. It is possible that within a few years, virtually every portion of computer hardware, from the display to the mass storage devices to the packaging for chips, will be fabricated by using some kind of masking process.
Each stage of the process, from preliminary design through fabrication, requires investment, skill, creativity, and just plain hard work. As the technology became increasingly important in the U.S. economy, additional legal protection at some stage of the process appeared to be necessary to protect this investment if innovation was to flourish.6 Beginning in the late