What the guy is handling is a standard "FPC" flexible board. These are basically fabricated just like ordinary PCBs, so the conductor is Copper - maybe tinned or with a silver layer. The main difference is that the traces are covered by cover layers to prevent shorting. (With some expertise, you can even peel off the cover layer.)
If you're very lucky, the carrier material would be Polyimide (aka Kapton), which can sustain temperatures up to 350 °C or so. Won't melt when soldering with moderate heat.

 

Sealed membrane keyboards are not reliable.

When it comes to non-mechanical keys, sealed membrane keyboards are at least better than anything non-sealed. Lifetime somewhat depends on the longevity of the elastomeric interposer layer, but at least the contacts cannot become contaminated. I've had worse constructions than this kind of sealed membrane keyboards.

 

They become self contaminated with time and heat.

I suppose they’re a reasonable design option. The problem is they’re largely custom and irreplaceable. I got 20 years or so out of mine. Not bad, but it’s unacceptable to trash an otherwise fine Jenn-Air oven because a stupid keyboard can’t be replaced.

 

No, to repair you need to separate layers.

Thank you for emphasising your point. I think I understand it now but please correct or approve of my understanding below.
What I was referring to was the "outside layers" what you are referring to are the keyboard membrane's "inside layers".

The "inside layers" are 3:

The back layers which has the brown electrical trace.​

The front layer which has the gray electrical trace.​

The above 2 layers are insulated from each other by the use of a middle insulating layer.​

Please see the picture below:
https://drive.google.com/file/d/1hivRxzvgyzauHE3VGALCJl2v68YsbkMB/view?usp=sharing

The above 3 layers can be separated from each other and then put back together (Is extra glue necessary to put it back together or the residual glue will be sufficient?). Separating the layers should not destroy the electrical traces. Conductive ink can be used to bridge any broken traces before putting the layers back together. (Is this description in line with what you are referring to as the correct repair method? Please elaborate, thanks.)

Can the same method that was used to separate the outside layers (ie use of heated feeler gauge) be used to separate the core layers of the keyboard membrane? Any tips you have to separate the core layers without damaging the traces? Thanks.

Can you recommend a few options to use to re-trace the broken traces with links to the products? Thanks.

 

Many places can print complete replacement units for you with minimal setup charges.

For reference can you provide links to these places and provide search terms. Thank you.

 

Here is some information I found about membrane switches from this website:
https://www.pannam.com/membrane-switches/

What is a “Membrane Switch”?​

A membrane switch is a printed electronic circuit that uses pressure to open and close a circuit. The membrane switch circuitry is most often screen printed using conductive inks, which are typically made of silver, carbon, and/or graphite.​

​

Membrane switches are part of a range of devices considered to be user interfaces (also called operator interfaces, or man-machine interfaces) along with display-based touch screens, and mechanical switches such as push-button, toggle, rocker, and slide switches. The ultimate purpose of a membrane switch is to serve as the interface between man and machine, enabling an operator to communicate with a piece of equipment, instrument, or machinery.​

​

Features & benefits of membrane switches include:​

Completely sealed surface – easily cleaned and sterilized​

Low Profile – no crevices that can trap contaminants​

A cost-effective alternative – less costly than rubber keypad assemblies and capacitive touch keypads​

Thin profile – saves valuable space in your product design​

Easy to interface with existing controllers – no special electronics required, as with touch screens​

Versatile graphic interface – overlays can be screen or digitally printed with stunning, photo-quality graphic effects​

Protection by design – Easier to protect from UV radiation than rubber keypads​

Water-resistant designs – meets NEMA 4 and IP 67 specifications​

How Are Membrane Switches Constructed?​

Membrane switches are essentially a sandwich of thin layers that are bonded together using pressure sensitive adhesives. Depending on the application requirements, a membrane switch will consist of as few as 4, and as many as 9 layers. In contrast to mechanical switches, membrane switches offer the advantage of lower cost, they consume less design space with their low profile, are easy to clean, and they offer a sleeker, ergonomic, and aesthetically pleasing appearance.​

​

The visible top layer of a membrane switch is the graphic overlay, with printed circuitry underneath the overlay. The circuitry can also incorporate different layers such as polyester (silver flex), polyimide (copper flex), and rigid PCB layers. Activation of a switch occurs when a printed shorting pad or metal dome makes contact with the bottom circuit layer thus, closing the circuit.​

 

Can the same method that was used to separate the outside layers (ie use of heated feeler gauge) be used to separate the core layers of the keyboard membrane? Any tips you have to separate the core layers without damaging the traces? Thanks.

Sad to say, but due to the vias in the membrane keyboard there's no way to separate the inner 3 layers without damage: separating these layers will break all these fancy vias! And I doubt they really can be restored.

 

Sad to say, but due to the vias in the membrane keyboard there's no way to separate the inner 3 layers without damage: separating these layers will break all these fancy vias! And I doubt they really can be restored.

Yes they can, they are only blobs of ink.

Is there a middle ground to the 2 above quotes?
(By the way what is vias? Are you referring to the hashed electrical traces behind each button?)
The middle ground I am asking about is this: without separating the entire layers only separate the little portion near the breaks at the button of the ribbon, or scrape the plastic there and re-ink the traces and then repair the plastic with something like crazy glue.

 

Can the same method that was used to separate the outside layers (ie use of heated feeler gauge) be used to separate the core layers of the keyboard membrane?
I suppose so, same adhesive was used on all surfaces. Usually the layers delaminate with a shearing sound when pulled apart.

The outer thick layer had a lot of globby glue (I made the mistake of trying to "clean" it, there was no need to clean it as I believe it can be reused, now with the cleaning it has less adhesive and will be weaker when put back together, my mistake so if anyone attempts this repair my advice is NOT to clean the glue off), the outer thin layer also has the same glue but less of it. In the description of one of the websites about keyboard membrane construction it was stated that the "core layers" use pressure sensitive adhesive (I think this is similar to the noteitpads adhesive) which I think is different from globby adhesive used for the outer layers, or if it is the same, a lot less of it is used in these core layers.

Also last night I wrote to a bunch of manufacturers doing these types of printing. If I receive any useful replies I will share them here.

 

I just checked to see if the electrical layers can be separated right now.

My first impression: It seems the electrical layers are "fused" together as one layer and then glued to the last outer blackened layer that has the labels. If this can be separated I doubt if it can separated by crude methods like heated feeler gauge as the layers appear extremely thin and fused as one. I need to research this and wait for the replies from the manufacturers too.

Right now my mind is in a bit of a blank.

anniel 747 have you ever separated these type of electrical membranes? If so how old were the ones you separated? Perhaps age and oven's heat makes the layers stick with a lot stronger bond. If the initial process of separation can be started then it might be a lot easier to pull them apart but how to do that initial separation?

 

As for tinting the board back, I found the following article:

How to Tint Eyeglasses Using RIT​

If you have an old pair of prescription glasses you would like to tint but you do not want to spend a lot of money having them professionally colored, you can try RIT dye at home. RIT dye is designed as a fabric dye that you can use at home, but it is also effective on plastic. Therefore, you can use it to tint your eyeglasses as well. The tinting process will only work on plastic eyeglasses. The results depend on the type of plastic, how long you leave the eyeglasses in the RIT dye and what type of coating is on the lenses.​

​

Bring 2 quarts of water to a low simmer on the stove in an old saucepan that is large enough for your eyeglasses to fit inside. Stabilize the temperature at a very low setting. If the temperature is too high, the plastic may melt or warp.​

​

Add 1 ounce of RIT dye and 5 drops of distilled white vinegar. Stir well.​

​

Submerge the lenses or eyeglasses in the dye solution. Make sure they are completely covered by the dye.​

​

Check the glasses every few minutes to make sure the eyeglasses are not being warped or melted. Do not go longer than 10 minutes between checks.​

​

Leave the lenses or glasses in the dye on the stove until the tint is as dark as you want. You can leave them for as little as 10 or 15 minutes for a light tint and as long as an hour or more for dark tint.​

​

Remove the glasses when the tint is as dark as you desire. Rinse the lenses or glasses in warm tap water then in gradually cooler water until they are completely cool. Dry them with a soft cotton cloth. Reinstall the lenses if necessary and your tinted glasses are ready to wear.​

​

You can tint your eyeglasses with RIT in a bucket using water that is hot initially but will cool, of course. The tinting process will take longer because of the lower temperatures.​

​

Dye other plastic items such as buttons with RIT.​

​

Clean up all the equipment you used immediately after the tinting process so that the RIT dye does not stain your utensils. Some plastic items may need to be soaked in bleach to get rid of the color. Try to use metal whenever possible.​

I don't know if this would work well on this plastic board as in the article it is stated different plastic react differently to this process. If anyone knows more please share. Thanks.

 

Some around 40 years old or more, others freshly printed and defective.

Since you seem to have extensive experience in separating these layers, can you go into as much details as you can on HOW you separate these layers? What equipments do you use? What tools? Do you heat the layers first or do any other preparations? Thanks.

How would you match the color and tint? You would also need to control the contour.

I don't know the answer to these questions. I posted the article to get feedback about it and start a discussion that may help me accomplish re-tinting the screen of this board. Perhaps you can shed some light on the subject yourself. Thanks.

Regarding soldering the ribbon cable to repair the broken traces: I had a piece of microwave keyboard membrane that I used for practice. Using this practice run as the gauge, with the equipment that is available to me it is NOT possible to go the soldering route to repair this ribbon. So there has to be some other method used for this repair.

 

I have seen some that have a few ultrasonically fused cross checkered dots to them.

Were you able to separate these ultrasonically fused layers also? How did you do that? Please go into as much details as you can. Thanks.

 

E-XACTO #2 #22 #23 #25 #28 and force, no heat. Stubborn ones get a trip to the freezer as this type of pressure adhesives loses strength in lower temperatures.

Great tip. I just put the board in the freezer. I took it out to take a picture for this post and it had wrapped. Should it be placed under something in the freeze to prevent warping? Will it go back to being straight once it goes back to room temperature?

I have to get an EXacto knife. They have a Zirconia Xacto knife that on the package of it they claim to be sharper and more durable. Do you have any opinion on this? Is the Zirconia Xacto knife worth the extra few dollars?

Another question about the layers:
I have taken 2 outside layers as was shown and discussed previously (the outermost was thicker and then the second layer which was thinner).

What I see now are 2 other layers:

the layer with the electrical sandwich layer with the two trace layers and the insulation layer in between​

the layer which contains the labels​

Please see the following pictures which show these 2 layers:
https://drive.google.com/file/d/1PqI7u4psdTX6Sq5aSdYJBxWwudp33Cuu/view?usp=sharing
https://drive.google.com/file/d/1pjNU7oKV4b79BPb4JMFdENs1StA4ASTs/view?usp=sharing

It seems I can separate these last 2 layers pictured above using my previous method of a hot feeler gauge, but then I need to proceed to take apart the electrical traces sandwich layers.

Is the following the way I need to proceed once the label and electrical sandwich layer are apart?

Separate the outer label layer from the electrical layer, then try to separate the electrical sandwich layers into 3 layers that consist of the 2 trace layers and the insulation layer. Before attempting to separate the electrical layers freeze the board, then use Xacto knife and force the corners apart, once the layers start to separate then use gentle force (DON'T go near traces or via(s) with the knife).​

​

For damaged filters I use my Rosco color swatch to exactly match the original.

Are you saying your spray painted the display? If so what exact colors did you use to get the tint? By the way there are 2 shades of tint on this display, one is darker than the other as shown below:
https://drive.google.com/file/d/1QF3PWDBICjjUWyQdqgYiZLNhIGGVQC5m/view?usp=sharing

 

Can you also link to an Xacto knife set that you think is a good deal and you use? Thanks.

 

Do you have a picture of the warping?

Yes see the following pictures:
https://drive.google.com/file/d/1UmWN5JJmavKR6vf2ddae08Ot9XPa1eMb/view?usp=sharing
https://drive.google.com/file/d/13t0MoaP1Ycve-U88lwehkXdPpQ6YLt1I/view?usp=sharing
https://drive.google.com/file/d/1Iu9OxaxBAVWDVintUvZ30-nAAJH1hr9a/view?usp=sharing

Another question about the layers:
I have taken 2 outside layers as was shown and discussed previously (the outermost was thicker and then the second layer which was thinner).
Useless.

I see your point. It was possible to go directly to the electrical sandwich layers, but I was not aware of how the membrane was constructed and where the electrical layer was. Even now I am not sure if I would do it differently because to go directly to the electrical sandwich layer seems more risky and likely to cause more damage to the traces. I think it would be VERY DIFFICULT to find the edges of the electrical sandwich layer amongst 3 other layer. As is, with 2 layers off, I still can't gain access to the electrical sandwich layer. I am hoping an Xacto or similar sharp tool can aid in this process. This is just my thinking, but I don't have the experience to back it.

Now necessary to repair the damaged filter, yes.

So separating the outermost layer which has the oven's labels from the sandwich electrical layer is not necessary either for taking the sandwich layer apart or to re-tint the outer layer. Is this correct?
Does taking these 2 layers apart makes the job of separating the electrical sandwich layer any easier?

Are you certain it's a filter, not opaque?

Can you elaborate? What is the difference between filter and opaque? Here is the picture of the rubbed off tint from the plastic in case you need to refresh your mind how it looks:
https://drive.google.com/file/d/1gW_X_FqBn7Ymm_RO2ftN6xYTJx8liNrD/view?usp=sharing

The colors that match my swatch book. Some are red or pink others green or blue, still others are orange, yellow, grey or violet.

I am not familiar with Rosco. Do they sell tint films that can be placed on a display? Can you describe the process that you use to re-tint a display like this using Rosco products? Also can you discuss the cost? Can anyone buy from Rosco? Thank you.
https://drive.google.com/file/d/1gW_X_FqBn7Ymm_RO2ftN6xYTJx8liNrD/view?usp=sharing

 

As a practice run I tried to take apart the electrical sandwich layer of a microwave keyboard membrane that was lying around. I am glad I did as this was very educational and revealing. It also caused new concerns and questions.

The peeled electrical sandwich layer of this microwave has 3 layers:

• upper pads and wires layer
• lower pads and wires layer
• the insulation layer between the upper and lower pads layers that acts as the gap between these 2 layer (this gap functions as the on/off switch so when the operator pushes on a button he is bridging the gap or turning on the switch causing current to flow)

Please see the pictures below that shows the construction of this sample microwave keyboard membrane.
https://drive.google.com/file/d/1VLDuSy-2EBSuVMI6yJFcb0JodVlrnv7N/view?usp=sharing
https://drive.google.com/file/d/1FycLfrsfz3qmJFwESk3xTivn9899LQkv/view?usp=sharing

But besides the above layers there are 2 other wire trace layers that are independent of the above layers and each of these layers contain the 2 wire trace levels (upper and lower). One wire trace level is the upper trace for the upper pads layer and one wire trace is the lower trace for the lower pads layer. Please see the picture below to see these 2 wire trace levels.
https://drive.google.com/file/d/13Mi2uAcJcCUUNJUijibCGVV_0-7bsPwI/view?usp=sharing
https://drive.google.com/file/d/1FzsnTDstyGR0jNAXfqcykY4igB2CfQET/view?usp=sharing

There is continuity from the tip of the ribbon cable to pads as shown below, but there is NO continuity in between as the wires have their own insulating layer.
https://drive.google.com/file/d/1BZA99pvUy9c1LwSEJ5YvhiiOpniUjtJp/view?usp=sharing

The only way to access the trace wires themselves in either through scraping off their insulation similar to the way a multi stranded wire insulation is taken off, or to peel their layer also (not sure if this is possible, please let me know of your experience in this regard, thank you).
Please see the picture below that shows a portion of one of the trace wires that has been scraped off.
https://drive.google.com/file/d/1ViI4UuLPKLYUHs_7lVghXRwzQqugRYDo/view?usp=sharing

The material of the wire traces below their insulation appears to be metal but it is NOT possible for me to solder to them. Perhaps as shown in some online videos it is possible to solder to them but that seems to require better soldering stations that are not available to me.

Should the insulating layer of the wires be scraped off? Or is it possible to peel away this final layer of the wire traces to gain access to the traces themselves for repair?

Please share your thoughts and experiences. Thanks.

 

This is not the same construction as the other one. Same techniques as PCB repair are used. Simply follow IPC-7711B/7721B guidelines.

Thank you for your reply and the suggestion to follow the IPC-7711B/7721B. I will study this guideline later.

Can you please point out the differences between this sample microwave keyboard membrane and the other one I am working on for the Whirlpool double oven?

It seems to me after studying this sample that the wire traces are insulated independently from the pads on these keyboard membranes, regardless of the brand. This makes sense as they must be insulated independently in order for the membrane to function correctly. Therefore regardless of brand once the electrical insulation layer of one of these keyboard membranes has been peeled, still the wire traces remain insulated, hidden out of access and encapsulated in their own protective plastic.

So my question remains, how to proceed once the electrical sandwich layer of the membrane has been peeled, and how to repair the broken traces inside the plastic layer of the traces that are still protected by the last layer of plastic. Thanks.

 

Maybe drilling a few holes and mounting some pushbuttons is starting to sound better?

 

Maybe drilling a few holes and mounting some pushbuttons is starting to sound better?

Definitely the option of the push buttons is still on the table. At least with everything exposed it is much simpler to draw a wiring diagram based on the traces of the membrane.

I took the keyboard membrane from the freezer and tried to separate the electrical sandwich layer. This oven's keyboard membrane is definitely differently constructed from the sample microwave keyboard that I tried to separate its layers as a practice run. As was stated the traces are not metal (ink) which is both a blessing and a curse . The curse because the traces WILL break (I think this is inevitable) and the blessing because the repair seems easier than the solder jobs I have watched in online videos. It also does not require a high quality solder station.

Not sure if it was due to being left in the freezer making the plastic hard and brittle or a combination of that and hitting the hollow of the area of the pads where there was no glue to absorb the force I was putting on it the oven's keyboard membrane snapped and tore. (My explanation: possibly once it got to the hollow area of the pads the force I was putting on it was excessive and it snapped since there was no glue to absorb the force and so the force was transferred directly to the brittle plastic layer, the force itself was low but obviously excessive).

Initially the electrical layer of the oven's keyboard membrane was separating fine. But even before the tearing, the ink traces had broken. Then suddenly it gave way and tore up in an unexpected and dramatic fashion, as shown below.
https://drive.google.com/file/d/1nbVLUgaDdWs014bhen_oIHU651xr-8fW/view?usp=sharing

This keyboard membrane still looks salvageable to me, the tear is just another thing that needs to be repaired. In fact possibly due to this tear the repair is easier. You may ask why? Well if it had not torn where it did, by the time it had fully separated a lot more of the traces would have likely been in need of repair.

See the picture below that shows where the traces came off even before the tear to see what I mean:
https://drive.google.com/file/d/1MPmUqcrvK-rdXm8P16oGBDpmXVoc4zKd/view?usp=sharing

The repair to this membrane appears to be simpler than let's say soldering but a little time consuming. Once the traces are redrawn and the layers carefully put together then it maybe function just fine.

For a successful repair the right glue/tape and the right electrical ink pen are quite helpful, so please share you sources and any other thought you have on the subject.