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Engineer Blog

Strange Tales─Part1

Silicone Free Power Supplies

My name is Yoshiharu Itagaki. I may be over sixty, but as far as my older work colleagues are concerned I’m still a young whippersnapper. Nevertheless, time ticks on, and to stay healthy, I do volunteer work on my days off, clearing bamboo forest.

When you have worked with bespoke orders and modifications for as long as I have, you are bound to have encountered a few unusual requests that leave you scratching your head. At Kikusui, we accept any special order that is technically feasible, provided we can agree on budget, although we sometimes find ourselves building devices based on technical specifications alone without knowing what they will actually be used for. In this series I will discuss some unusual bespoke projects I have encountered at Kikusui, while maintaining our clients’ confidentiality, of course. Today’s instalment concerns a silicone-free power supply I worked on 20 years ago.

Hold the Silicone

The client in question asked for a power supply without silicone, much as one might order a hamburger without the pickles. As you may know, silicon and silicone are in fact different materials, with the former being the mineral used to build semiconductors, while the latter is a class of compounds including rubbers, resins, and oils in which silicon atoms are combined with organic molecules. Our client had requested us to modify a previously delivered device on the grounds that a gas emitted by silicones was somehow interfering with the user’s system.

We proceeded to replace the following silicones used in the direct current power supply with other compounds:

  • thermally conductive silicone grease
  • silicone tubing
  • silicone sheets (electrical insulation)

Silicon semiconductors were left as they were, as no alternatives were available. (Of course, as mentioned above, silicon and silicone are in fact different substances.)

As only a small number of devices were to be modified, rather than starting a brand new production lot, we simply dismantled made up power supplies that we had on hand, and replaced the silicone components before reassembling the supplies and conducting the necessary adjustments and performance. As someone who gets joy from satisfying his clients’ demands, I did not mind that the process took a long time.

Our biggest challenge was finding silicone-free thermal grease, which was not commercially available at the time. We eventually got hold of a silicone-free variety that was intended for either NASA or the US military. It cost 10,000 yen for a 10 centimeter tube, and we were careful not to waste it in case we got a repeat order.

A Mystery Solved

When doing research for this article, I was surprised to find that nowadays silicone-free products are readily available. Note that simply searching for "silicon-free" will bring up hits for shampoo, so when doing Internet searches you need to add search terms like "components" or "materials". Incidentally, many of the general public appear to use silicon and silicone interchangeably.

While 20 years ago I did not know why our client needed a silicone-free power supply, in my research I came across a phenomenon that seemed to solve the puzzle. It is likely that our client’s power supply needed to be silicone-free to prevent contact failure caused by low-molecular-weight siloxanes. Nowadays, we know that the low-molecular-weight siloxanes emitted by silicones can cause the terminals of relays and switches to fail. This happens because low-molecular-weight siloxanes deposited on the contacts oxidizes in the presence of arcing and turning to silicon dioxide, an electrical insulator. It is this silicon dioxide that causes contact failure.

Our made-to-order power supply was to be incorporated into a system used by the client. I surmise that the client needed to eliminate possible causes of contact failure in a long-term, sealed (perhaps unventilated?) application, and that they knew about the issues presented by low molecular weight silicones before everyone else did.

I still do not know what kind of top-secret system our client powered with their made-to-order power supply. Nonetheless, these "Mission Impossible" style orders are what makes the bespoke business so special.

Yoshiharu Itagaki
Solutions Development Division, Solutions Development Department

[Major achievements in product development]
PAL, PAK-T series regulated DC power supplies
Custom built regulated AC power supplies; made to order charge/discharge power supplies
Custom built electronic load devices; custom built bipolar power supplies, etc

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