Who invented the film resistor, and when ?
How are they made, and what is their internal structure ?
How do they put the color codes on them ?
Don’t know who invented them.
I’ve worked at 2 companies that made thin film metal film resistors.
TRW IRC evaporated the film on hollow ceramic rods that rotated around a metal film source.
The film is evaporated on the ceramic while inside a bell jar which is evacuated to a few microns
I only worked in evaporation a short time so I don’t remember much.
Precision Resistive Products uses a different method where the ceramics are tumbled inside a metal drum.
The film is evaporated from a rod which is wrapped with nickel wire.It is again done in a vacuum.
The resulting stock is binned by resistance value and TC.
Again the manufacturing differs.
TRW capped the resistors before spiraling them where as PRP spirals then caps.
Spiraling is done by abrasive wheel or laser cut.
Any trimming for R value comes next.
Again some differences.
TRW paint coated the ceramics next but PRP uses a varnish type material.Its for moisture.
They are then rolled over a wheel with a measured amount of powder coat to create the plastic outer coating.
PRP doesn’t make color coded parts.
At TRW the resistors were rolled over a series of wheels each of which were dipped in the appropriate color of paint.
Hope this helps
Well heck
Its been several years since I worked at either place.
TRW capped the resistors with the leads on the caps while PRP capped spiraled and then welded the leads on
sorry about the confusion.
Do a search on: Jack Gingold Film Resistor
From [www.ee.bgu.ac.il/~pec/L%25202.doc+jack+gingold+film+resistor&hl=en&ie=UTF-8"]this](http://216.239.57.100/search?q=cache:_5Pl2SZHWBUC:[url) nice website:
“Vacuum pyrolysis of hydrocarbon material vapors to form carbon films was reported by Sawyer & Mann (1880), and the hydrogen reduction of WCl4 to form tungsten films was reported by de Lodyguine (1897). Carbon film resistor was developed in 1930s in Germany by Dr. Jack Gingold (Rosentahl).”
Vacuum pyrolysis often involves thermal decomposition of constant feed, rod electrodes. Once they begin to arc, disassociation sets in. The rods are mechanically pushed toward each other to maintain a controlled reaction rate. If you decompose the carbon rods in a reactive atmosphere, or co-deposit it with an insulator, you can control the resistivity of the resulting film per given thickness. You may have seen a light bulb where the (failed) filament deposited an interior coating to the glass envelope. That is a similar physical deposition mechanism.
By placing the substrate (surface to be coated) a fixed distance from the pyrolizing source, controlling the carbon rods’ extension feed rate, maintaining a consistent drive voltage and current and keeping the chamber properly evacuated, a film of precise resistance can be deposited. This can be laid onto mylar film, cut into ribbons and wound up to any length like toilet paper.
I helped design tantalum pentoxide thin film resistor networks for the Space Shuttle program. They were fabricated on sapphire wafers. Deposited via inert and reactive gas sputtering, the process was easily controlled and the components inexpensive to manufacture. Ta[sub]2[/sub]0[sub]5[/sub] is easily passivated in an oxygen environment. This renders the resulting film surface inert and relatively impervious to chemical attack. Most of all, it prevents a lot of the potential drift in value. A pure metal network would have corrosion form on it over time. This would shift the resistor’s value as pure metal was replaced by less conductive oxides. By reactively pre-passivating the film before it is packaged, a significant chance for the component’s value to change or drift over time is eliminated.
Trimming a resistor structure in order to alter its value is a cost efficient production technique. It is done with everything from sandblasters or dicing wheels to high power fluorine lasers. Imagine a ladder type structure of passivated metal film deposited using standard photoimaging techniques. Use a tightly focused laser to vaporize links (rungs) out of the ladder. The current flow is connected so it travels down one leg of the ladder and jumps across the first available link (rung) to reach the other leg and then flow out of the resistor. Removing a link forces the electrical current to travel farther through the ladder’s resistive trace. The farther down the ladder current has to flow to reach the first unbroken rung, the more resistance the ladder structure exhibits. Electrically monitoring the circuit’s resistance while you trim it permits exact tolerancing.
Color Coding:
The sealed resistors are sorted into batches according to value. The batches are striped by a miniature rotisserie with multiple wheels that roll in preselected paints. The color code permits ready field identification of passive components without a meter. It is also easier to read than small digits printed on the component body.
fixed link
Thanks to both of you. Vacuum deposition on ceramic makes a lot more sense than the capacitor-like mylar-wrapped cores I’d visualized, and I’m surprised they still use paint to label them, rather than a printed shrink-wrap coating.