Touchscreen Polymer Layer Deformation Measurement

normzone

Trusted Information Resource
#1
Hello all. Thanks for all your help in advance. I've got a new inspection challenge.

We are seeing an artifact of manufacture in a touchscreen bonded to an LCD.

The touchscreen consists of a polymer layer attached to a piece of glass.

That assembly gets bonded to an LCD.

What we're seeing is that when the LCD heats up, the polymer layer of the touchsreen expands at a different rate than the glass it's bonded to, and in doing so swells up slightly in a mode we're referring to as "pillowing". It's not visible with text or image, but the customer is not happy.

Discussions are underway to quantify exactly how much of this phenomena is acceptable.

My challenge is how to measure the amount of deformation. It is visible only when the unit is at operating temperature. Contact measurement is going to be touchy at best, and I'm not familiar with any other techniques that would be appropriate.

I do have some budget available to address this issue, so I'm open to all suggestions.

Thank you all, Covers (would that more properly be Elsmarians?)

Norman
 
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Tim Folkerts

Super Moderator
#2
Re: Touchscreen layer deformation measurement

Some sort of optical testing seems like it would work. I am envisioning shining a light on the surface and seeing how it reflects. Something like this (where the diagonal lines are the light and the periods, —— is your surface, and the periods are needed just to maintain the spacing)


\\\\....////
.\\\\..////.
..\\\\////..
...\\\\//...
____—_______


If the the surface to be tested is flat (or even uniformly curved), the reflection from the glass/polymer surface should be uniform. If the surface is "pillowed" then the reflection would get distorted. For instance if the surface being tested was a rectangular sheet, you should see a rectangular spot on the ceiling. If the spot is patchy or the edges are distorted, the surface has imperfections.

You would have to find a way to quantify the quality of the reflection compared to know quality of surfaces. You might be able to do this by eye, or perhaps digitally image the reflection to see how uniform the reflected patch is.

This is just brainstorming -- I don;t know of such a device commercially available.
 

Jim Wynne

Staff member
Admin
#3
Re: Touchscreen layer deformation measurement

Hello all. Thanks for all your help in advance. I've got a new inspection challenge.

We are seeing an artifact of manufacture in a touchscreen bonded to an LCD.

The touchscreen consists of a polymer layer attached to a piece of glass.

That assembly gets bonded to an LCD.

What we're seeing is that when the LCD heats up, the polymer layer of the touchsreen expands at a different rate than the glass it's bonded to, and in doing so swells up slightly in a mode we're referring to as "pillowing". It's not visible with text or image, but the customer is not happy.

Discussions are underway to quantify exactly how much of this phenomena is acceptable.

My challenge is how to measure the amount of deformation. It is visible only when the unit is at operating temperature. Contact measurement is going to be touchy at best, and I'm not familiar with any other techniques that would be appropriate.

I do have some budget available to address this issue, so I'm open to all suggestions.

Thank you all, Covers (would that more properly be Elsmarians?)

Norman
This kind of dimensional measurement can get very expensive if you want to buy the equipment to do it. You might want to think about contacting a local metrology lab that has something like this or some other form of laser/white light scanner.
 

normzone

Trusted Information Resource
#4
Re: Touchscreen layer deformation measurement

Expensive indeed. My boss just asked me to see what I could do for $5K - I didn't have the heart to tell him. I said I'd look around.

I figure with a height gage and a surface plate and a unit at operating temperature I can go for contact until deformation of the deformation (DOTD) becomes evident, and then compare that to a non-deformed zone (NDZ) contact point.

But the area of uncertainty includes both the amount of contact required to create visible DOTD and the unseen/unfelt amount of contact in the NDZ.

I think my boss was expecting me to produce a ray gun that would display true values in the production area.

EDIT: Well, I guess this constitutes a happy ending. The people who make the laser equipment that [Jim Wynne] suggested (thanks again Jim) do their manufacturing right around the corner from us. While it's a bit pricey for my budget today they are going to bring their service to us for a fee and get us some numbers. This should be fun.

Thanks all who viewed or posted -
Norman:bigwave:
 
Last edited:

normzone

Trusted Information Resource
#5
Re: Touchscreen layer deformation measurement

Some sort of optical testing seems like it would work. I am envisioning shining a light on the surface and seeing how it reflects. Something like this (where the diagonal lines are the light and the periods, ?? is your surface, and the periods are needed just to maintain the spacing)


\\\\....////
.\\\\..////.
..\\\\////..
...\\\\//...
____??_______


If the the surface to be tested is flat (or even uniformly curved), the reflection from the glass/polymer surface should be uniform. If the surface is "pillowed" then the reflection would get distorted. For instance if the surface being tested was a rectangular sheet, you should see a rectangular spot on the ceiling. If the spot is patchy or the edges are distorted, the surface has imperfections.

You would have to find a way to quantify the quality of the reflection compared to know quality of surfaces. You might be able to do this by eye, or perhaps digitally image the reflection to see how uniform the reflected patch is.

This is just brainstorming -- I don;t know of such a device commercially available.
I've long since left that organization and now play for a competing team, but I came across this thread today and wanted to postscript it.

What one of our engineers came up with was a variant of what [Tim Folkerts] described above. The contraption viewed the deformity developed at an angle and bounced that image expanded up to a grid that allowed us to quantify the expanded amount of deformity, and we took a picture as well.

Splitting hairs with light and mirrors...
 
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