Turning to Chemistry for LCD Panel Polarizer

I thought it might be fun to salvage the polarizer from a broken laptop LCD screen, but it has put up quite a fight. I first tried direct mechanical brute force and managed to shatter the glass. Thankfully, not injuring myself doing it. When physical power doesn’t cut it, we turn to chemistry.

The risk of this approach comes from the fact the polarizer is made of plastic of unknown composition. Ideally I could find a solvent that will dissolve the adhesive and leave the plastic intact. If I was better at chemistry I might have some methodical way to find that solvent, but all I’ve got is trial-and-error. To aid in the trial-ing (and the error-ing) I have a portion of the polarizer I’ve already freed from brute force, carrying with it a layer of tacky glue. It’s enough for me to get started.

I had a rough progression of least- to most-aggressive solvents. First up to bat was 70% isopropyl alcohol, and the glue just laughed at its feeble efforts. After I let the alcohol dry, I tried WD-40, which also did nothing. I wiped up as much of it as I could before moving on to the next contestant: Goo-Gone.

Goo-Gone had some effect. It did not magically dissolve the glue as it tends to do with most other glues I come across, but it did soften this stuff somewhat, and it didn’t seem to damage the plastic. Using Goo-Gone to soften the glue, I was able to peel the sheet of polarizer free of the remaining glass and finally freed myself of the risk of puncturing some body part from thin pieces of broken glass.

However, that’s only half a victory as the glue remained stubbornly attached to the plastic making it unusable for light polarization fun. More Goo-Gone only seemed to spread it around and didn’t dissolve it. So I moved on to the next item: mineral spirits. It further softened the glue enough for me to start rubbing them off the plastic. It was a very labor intensive process, but I could start to see the shiny surface of my polarizer sheet. But I soon reached the limits of this approach as well. I started sensing uneven bumps in the surface and I couldn’t figure out what’s going on until I dried off all the mineral spirits for a look.

It appears there are multiple parts to this glue, and there is a much tougher component that clung on to the film. They were applied in lines and that explained the ridges I could feel in my fingertips while this film was damp with mineral spirit.

Finding the limits of mineral spirits for this task, I moved on to acetone a.k.a. nail polish remover. This is something I knew could melt certain plastics, as it’s used to smooth and weld plastic parts 3D-printed in ABS. However, I also knew it is not equally destructive to all plastic, as it seems to do very little (or absolutely nothing) to 3D-printed PLA parts and acetone itself sometimes comes in plastic bottles. Lacking experience in identifying plastics, I proceeded on my trial-and-error process.

The good news: using a small amount of acetone in a test corner, I found that it quickly dissolved the adhesive, turning them into soft goop that are trivial to remove. Wiping it off, I see the clear surface of polarization film with no evidence of chemical etching or erosion. I think this is the ticket!

But then I went too far by soaking the entire sheet in acetone, expecting to pull out a completely clean polarizer. When immersed in acetone, the polarizer film became brittle and cracked into little pieces. It marked the end of this experiment, but next time (I’m confident there’ll be a next time) I’ll try a few intermediate steps to see if I can find a good point on the spectrum between “few drops in a corner” and “soaking the entire sheet.”

Trying to salvage something from this screen’s LCD module was a bust, but I still have a very fascinating backlight module to play with.

Layers of Glass in LG Laptop LCD

I have a broken laptop LCD display module that I’m taking apart. It is a LG LP133WF2(SP)(A1) and it came from a Toshiba Chromebook 2 which was retired due to said cracked screen. I was able to split it into its two main components, the backlight and the display, both connected to the integrated driver circuit board. The backlight connector was something I could disconnect and reconnect, which is not something I could say for the high density connectors to the front display panel. Fortunately the screen is already cracked and nonfunctional so the majority of risk of disassembly is from broken glass.

The edge of this display module made it clear there is a complex multi-layer sandwich within.

There are at least three layers. The topmost layer is very thin and feels like plastic. The middle and bottom layers feel like glass. They don’t come apart easily, so I thought I’d try peeling the top plastic layer like a sticker. It is indeed backed by some adhesive, pretty tenacious ones at that.

I tried to keep the glass layers as flat as I could while I peeled, a difficult task with the strength of that glue which resulted in some alarming flex in the glass. I double and triple checked to make sure my eye protection is in place while peeling. After several centimeters of progress, scary bending and all, I felt a “pop” as the flexing freed whatever had held the middle and bottom glass layers together around their edges. Once this corner popped free, it was trivial to travel around all edges to peel the two glass layers apart.

It was damp between these two layers, presumably a thin layer of the “liquid” in Liquid Crystal Display (LCD). It was easily absorbed by a single sheet of paper towel, and its oily residue cleaned up nicely with 70% isopropyl alcohol. As far as I know, this is not a toxic material and I had not just cut years off my life, but I went and washed my hands before proceeding.

The bottom layer is where the original crack had lived, and these cracks had gotten worse due to the recent flexing. I don’t see anything of interest in this layer so I set it aside for safe disposal.

The two glass layers each had a grating that can be barely felt with my fingertips. They are also visible if I shined light through each layer. They are orthogonal to each other which would make sense if one set controlled horizontal pixels and the other controlled vertical pixels. Also, once the two glass layers separated, I was able to confirm the passive polarization filter (one of the objectives for salvaging) is the flexible sheet of plastic I had been tugging on. I resumed peeling that layer but didn’t get much further. Now that I only have one glass layer instead of two, it shattered under stress.

Even though I expected this as a potential (likely, even) outcome, it was still a surprise when things finally let go. Three cheers for eye protection! I picked out a few tiny shards of glass from my fingertips, but none of them found a blood vessel so there was no bleeding. And I think I managed to collect all the pieces scattered around the table. I had thought this would be a minor setback and I could continue peeling but just with smaller pieces of glass, but I was wrong. I don’t know my glass properties very well, but something happened here to change the mechanical properties of the glass. Once the first break happened, it has almost no strength at all. Continuing to peel — even at a lower force — causes new breaks. Brute strength will take me no further. And when brute strength fails, I turn to chemistry.

LCD Panel Driver Circuit Board

I’m taking apart a broken laptop LCD panel, a LG LP133WF2(SP)(A1) from a Toshiba Chromebook 2. I started with the very fancy tape surrounding the edges. Once the tape was gone, its top edge started unfolding into two parts. But they’re still held together on the bottom edge with the integrated driver board for this display. So I should figure out what that’s about before trying to completely separate the two parts.

The front side of this board had three sets of extremely high density connectors to carry signal for all 1920×1080 pixels on this module.

The back side of this board had all of the integrated circuits and a lower density connector for the backlight.

A single cable carried both power and data from the laptop mainboard. The chip closest to that connector was the largest IC on this board and probably mastermind in charge of this operation.

A search for “LG ANX2804” came up empty, which is not a huge surprise for a chip designed and built by LG for internal consumption by their display division. There’s no reason for them to distribute specifications or datasheets. On the other side of the board we see a connector for the backlight. The connector has nine pins, but in the ribbon we see six thin wires plus a wider seventh wire. This wider wire consumes two of the nine pins, making it a good candidate for either a common anode or cathode for LEDs. This left one pin in the connector seemingly unused.

I had expected just two wires for a simple string of LEDs, but the backlight is evidently more complicated than that. I’m optimistic I can get this figured out because the IC closest to this connector is clearly marked as a TPS 61187 by Texas Instruments, and I hope the information available online will help me sort it out later.

Returning to the front of this board, these high density data connectors are fascinating but I don’t understand everything that’s going on here.

I count somewhere between four and five contacts within a millimeter. This is definitely beyond my soldering skill, but they aren’t soldered anyway. Whatever this type of connection is, it is clearly single use. Once I detach it (it peeled off like tape) there’s no way for me to reattach it. I see nothing to help me align the connector. I’m also curious about the fact the copper contacts area is wider than what we see actually used. I’m sure it’s a provision for something but I don’t know what. For today it doesn’t matter, as the screen is already cracked and nonfunctional so I lose nothing by peeling them off before I explore its intricate layers of glass.

LG LCD Panel LP133WF2(SP)(A1) Teardown

After I checked the USB OTG reader off my teardown to-do list, I decided to continue ignoring what I had originally planned to do and continued tearing down another item that’s been sitting on my teardown to-do list: a broken LG LCD panel LP133WF2(SP)(A1). It was the original screen in a Toshiba Chromebook 2 (CB35-B3340) which I received in a broken state with the screen cracked. I revived the Chromebook with a secondhand replacement screen, and I set the original cracked screen with the intent of eventually taking it apart to see what I can see. “Eventually” is now.

Out of all the retired screens in my hardware pile, this was the most inviting for a teardown due to its construction. The ever-going quest for lighter and thinner electronics meant this screen wasn’t as stout as screens I’ve removed from older laptops. I noticed how flexible it was and it made me nervous while handling it. Most of the old panels I’ve handled felt roughly as rigid as a thick plastic credit card, this display felt more like a cardboard business card. I’m sure the lack of structure contributed to why the screen was cracked.

The primary objective of this exercise is curiosity. I just wanted to see how far I could disassemble it. The secondary objective is to see if I can salvage anything interesting. While the display itself is cracked and could no longer display data, the backlight was still lit and it would be great if I could salvage an illumination panel. And due to how LCDs work, I know there are polarization filters somewhere in its sandwich of layers. I just didn’t know if it’s practical to separate it from the rest of the display.

The primary concern in this exercise is safety. The aforementioned quest for light weight meant every layer in this sandwich will be as thin as it can possibly be, including the sheets of glass. And since the screen is visibly cracked, we already know this activity will involve shards of broken glass. I will be wearing eye protection at all times. I had also thought I would wear gloves to protect my fingertips, but I don’t have the right types for this work. All the gloves I have are either too bulky (can’t work with fine electronics in gardening gloves) or too thin to offer protection (glass shards easily slice through nitrile.) I resigned to keeping a box of band-aid nearby.

All that said, time to get to work: around the metal frame this panel is surrounded by a thin black material that contributes nothing to structure. It’s basically tape. Cut to precise dimensions and applied with the accuracy of automated assembly robots, but it’s adhesive-backed plastic sheets so: tape.

The adhesive is quite tenacious and it did not release cleanly. Once peeled, the top edge of the LCD array could separate from the backlight. The diagonal crack is vaguely visible through the silvered mirror back of the LCD.

This is a good start, but I can’t pull them apart yet. Right now they’re both connected to this panel’s integrated driver circuit board.