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Typical keyboard material

Discussion in 'Hardware' started by LapisLazuli, May 23, 2017.

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  1. LapisLazuli

    LapisLazuli Thread Starter

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    Good day everyone,

    I am trying to find what are the materials used in making the components of a membrane switch keyboard ( specifically a genius series KB110 keyboard).

    I have looked it up myself, however, what I found is a broad answer of plastic, instead of the specific material.

    The key matrix and the PCB materials are my main points of interest, I would like your help on the matter.

    Sorry if this is not the place for this type of topic.

    All the best
    Lapis
     
  2. kenbok51

    kenbok51

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    The plastic is likely Low Density Polyethylene or LDPE. Its more flexible than the high density plastic that hard toys are made of so can be quite flexible. That's not to say that other materials could not be used or a combination of plastics. Think squeaky toys that can be very pliable. It functions as a dome is created over each switch on the PCB which has a striped circle of not connected but conductive material (think about putting your right hand fingers between your left had fingers with out them touching each other). Inside the dome is also conductive material (can be carbon) and when the dome is collapsed it makes a connection on the PCB board at the point of the striped circle completing the circuit. The plastic used in remote controls is similar but the buttons are more sharp at the top than domed and underneath it a recessed finger with carbon on it that when pressed down contacts the board.
     
  3. kenbok51

    kenbok51

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    PS they also use silicone. That slipped my mind last time. The doming of the plastic allows it to act as a switch since when pressed down it will pop back up when released. The best keyboards use actual switched called cherry switches if I'm not mistaken.
     
  4. LapisLazuli

    LapisLazuli Thread Starter

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    Thank you very much for your help.
    After conducting more research on the key matrix I have found that the material of the lines is Silver plated carbon, however, I still do not know the material of transparent plastic the lines are on, do you have any idea?
     
  5. kenbok51

    kenbok51

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    Are you talking about the PCB clear coating or the keyboard flex pad? I assume your thinking about recycling materials. I used to be in plastics recycling and your asking the same kind of questions we did.

    here are a few hints for you:
    http://hackaday.com/2013/09/20/polyurethane-protecting-pcbs/
    If your trying to make your own
    and
    https://en.wikipedia.org/wiki/Conformal_coating
    For more details

    the wikipedia page has a ton of reference links at the bottom of the page that may help although some of them are PDF's. For Manufacturing coatings I would suspect UV treated epoxy.
     
    Last edited: May 26, 2017
  6. LapisLazuli

    LapisLazuli Thread Starter

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    [​IMG]
    I am talking about the part that is directly attached to the rubber domes, you can see it in the image above. I need to find the material of the sheet the lines are on, which I think is Polypropylene (PP), but not ver sure about it, and if it is that material, are all three layers the same material?
     
  7. kenbok51

    kenbok51

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    The main bulk of the pad is probably silicone but I don't see the need for three layers just two. The copper lines and dots are probably printed right onto the final sheet (PP or maybe HDPE) on the other side that's shown. Then that sheet is bonded to the silicon main body. The printed sheet could be anything since it doesn't have to be flexible. PP is not very long lasing especially when exposed to sunlight or heat. Next would be PVC (polyvinylchloride) and then PC (polycarbonate the toughest). PC is the most expensive material. Unfortunately there is only one way I learned to identify these plastics. You would have to remove some of it and burn it to smell the smoke it produces. PVC is easy, it burns the nose when Chlorine gas is released. HDPE smells like you just blew out a candle like wax smoke (LDPE is the same). PP is similar to HDPE but has an added perfume like smell. And Polycarbonate smells like your ironing linen. I'm sorry I can't be more specific without having some to play with but I assume not all manufacturers use the same materials. There is a thing called a "material safety data sheet" that manufacturers are supposed to let you examine if you ask. It's worth a try, give them a spiel about a report you need to do on keyboard material safety and see if they fall for it. I think its a law they have to supply it on request, at least it used to be.
     
  8. kenbok51

    kenbok51

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    I forgot one, PETE or what they make pop and water bottles out of (Polyethylene Terephthalate) it's both strong and flexible especially when thin.
     
  9. LapisLazuli

    LapisLazuli Thread Starter

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    That was a great analogy! I have done the test and think the material is LDPE.
     
  10. kenbok51

    kenbok51

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    It could also be HDPE since when it's thin it can also be flexible. Also there are what's called different melts or melting points that differentiate between types of HD and LD polyethylene. But they are very similar since the only difference between them is density (the D). That is to say if your talking about the thinner sheet with the circuitry printed on it which appears to be bonded to the main body that allows the key presses to spring back. That doesn't mean that they are necessarily different materials just different pressings or moldings that are joined together to create the whole effect as well as perhaps different melts or densities. Well, now you know almost as much as me at identifying certain plastics by their fumes.
     
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