What are semiconductors?
Originally, semiconductors got their name as materials with properties somewhere between “conductors” (materials that conduct electricity, e.g. gold, copper, etc.) and “insulators” (materials that do not conduct electricity, e.g. glass, rubber, etc.). The semiconductors are “materials that exist in between” (silicon, germanium, etc.). Those electrical properties are used to produce electronic control parts. Today, these products are collectively known as “semiconductors” and include products such as transistors, IC (Integrated Circuits) and LSI.
In Japan, products that become the foundation of industry overall and an essential part of life are called the “rice of industry.” During the period of rapid economic growth, steel was referred to in this way. However, from the late 1970s onwards, semiconductors became the “rice of industry.” Nowadays, semiconductors are used in all kinds of products. This of course includes electronic equipment and communications equipment, but also includes other products such as household electrical products, entertainment devices, automobiles, robots and cameras.
The plating in the manufacturing of those semiconductors differs from normal plating in several ways. Let’s focus on those differences.
Detailed circuits (fine patterns) that are beyond imagination
One representative semiconductor product is the IC (Integrated Circuit). Advances in manufacturing technology have produced finer and finer patterns on these IC. One famous rule regarding the production of finer patterns is “Moore’s Law.” In simple terms, Moore’s Law states that “the capacity of integrated circuits doubles every 1.5 to 2 years.” The products produced have more or less followed this rule from when the law was proposed in 1965 up to the present day. This has been realized by dramatic decreases in the wire width and wire interval (pitch) inside the integrated circuits. At present, wiring is produced that measures several nm (Nanometer: 1 nm is one billionth of a meter), but that production is becoming more difficult by the day.
The plating used in the surface processing of the electrodes on the outermost surface of IC chips includes processes such as electrolytic copper, electrolytic nickel, electrolytic tin-silver, electroless nickel, electroless palladium and electroless gold. This plating is one major driving force for the continuing evolution of semiconductors.
Plating in a cleanroom
In the manufacturing of semiconductors and the fine detailed plating that it requires, it becomes necessary to consider the working environment. Plating work at the sites of semiconductor manufacturing must be performed inside a cleanroom.
A cleanroom is a room where the number of dust particles in the air is controlled. One method we use to describe how few particles of dust there are is to describe the environment as “Class **.” The “**” that follows the class is a number. This number is used to express the number of particles in a cubic foot (Cubic foot: Approx. 30 cm × 30 cm × 30 cm).
It is said that “Class 100” or less is necessary when manufacturing semiconductors. In general, the outside air is said to be equivalent to “Class 1,000,000,” so this means that the work is performed in an environment with one ten-thousandth the dust of the outside air.
When the pitch is reduced to the nanometer level as I said in the section above, dust becomes a cause of trouble. For example, shorts (when two wires are short circuited or joined together) and circuit defects can occur. This is why it is necessary to perform the work in a cleanroom, where there will be no effects from unnecessary items such as dust.
The plating solution must also be clean! (The filtering of plating solution)
I have explained how it is necessary in the manufacturing of semiconductors that we are careful about the working environment where the plating is performed. In the same way, it is also unacceptable for there to be any fine dust particles mixed into the plating solution itself. For this reason, when plating solution is used, it is necessary to filter it.
This filtering is performed to remove the dust and other particles from the solution. At a plating factory, this is performed with filtering equipment.
There was a time when it was said that filtering plating solution would cause the solution to separate so that it would become unusable. Nowadays, however, the filtering of plating solution is the norm when performing plating in this kind of manufacturing and precision filtering is performed for the plating on semiconductors.
Plating in the spotlight in recent years
Palladium plating has been used for some time on points of contact such as connectors, but it could not match the excellent performance of gold plating. However, the rise in the price of gold in recent years has led to a reconsideration of palladium plating. It is now starting to play a leading role in efforts for gold replacement (to not use gold and to use a different metal instead) and gold reduction (to reduce the amount of gold used).
In many cases today, palladium or an alloy of palladium, nickel and silver is used.
In other uses, it is also often used as the barrier layer when performing gold plating (as the layer to prevent the corrosion of the gold plated layer by other metals) and as a catalyst (to promote the reaction of specific materials).
Due to environmental problems, there are demands to avoid the use of heavy metals whenever possible. These metals are harmful to the human body and their disposal places a burden on the environment. On electronic components, one major issue has been the use of the lead that is included in the solder used to connect components. A shift to lead-free solder is now in progress. As a result, electroless tin plating and tin alloy plating are attracting attention as plating that can perform the role of the solder without the inclusion of any lead. Tin has always had good solder wettability (good adhesiveness to solder). It is used as the plating on connectors and also for applications such as tableware, as a metal that has no effect on the human body. It will no doubt continue to be used in large amounts in the future.
Fuel cells are attracting attention as a system of electricity generation that is gentle on the environment. This is a system that creates water and electrical energy out of hydrogen and oxygen, by using the reaction that is the reverse of the electrolysis of water (the application of electrical energy to water to split it into hydrogen and oxygen). Platinum electrodes are used at the very center of this system.
However, platinum itself is extremely expensive, so it will become necessary to reduce the amount used before moving to the mass production of the systems. There are great expectations for technology using plating to manufacture the electrodes with an amount of platinum that is far smaller than that normally used.
Although I have not been able to introduce this today, semiconductors are also used for solar cells and plating plays a role there too. For fuel cells too, as I have explained, there are things that we will be able to realize through plating.
When we consider problems such as global warming, one key point for the technologies from now onwards will be whether we can supply energy more efficiently and more cheaply. Development is ongoing so that plating will be able to play a role in this and be useful in the future solution of energy problems.
There is a future that can only be created with plating and contributing to the solution of energy problems is one part of it.