Graphics LCD, Flex Tail, "Hot Bar" soldering...

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I am looking at several GLCD's for a one-off project, and Crystalfontz has quite a selection, such as this one: 240x320 RGB, 8-bit interface, 3V .

The description states it has a "flex tail" and is designed to be soldered to PCB pads using a "hot-bar" soldering machine.

Question is this: Can I hand solder this to a PCB using my "normal' soldering iron that I use for through hole and SMD PCB soldering :?:

I've seen what appear to be "flexible stips" on the LCD's of inexpensive calculators. Trying to solder one of those was a disaster... The entire thing kind of melted, as I recall...

Wiki Hot Bar Soldering says:
Hot-bar reflow is a selective soldering process where two pre-fluxed, solder coated parts are heated with heating element (called a thermode) to a sufficient temperature to melt the solder.

Pressure is applied through the whole process (usually 15 s) to ensure that components stay in place during cooling. The heating element is heated and cooled for each connection. Up to 4000 W can be used in the heating element allowing fast soldering, good results with connections requiring high energy.

My work bench soldering iron is a bit shy of 4000W !!!

If anyone has some thoughts / words of wisdom / suggestions / or guidance I'd appreciate hearing about it.

JC

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I've never come in contact with that kind of connector, but from what I understand it's quite similar to the "flexible strips" on LCD's you mention, JC. That means they'll be pretty tricky to successfully solder, because they're not only subject to heat, they seem pretty small too.
There ought to be some companies in your area that do prototype work - if asked nicely, they might be able to help.

The 4 kW heating element is... well, probably partly wikipedia being wikipedia. Also, your soldering iron only heats one pad at a time, so 15-40 W (which I guess are pretty standard powers for bench units) is quite enough then. This thing has to heat multiple pads, all at the same time and at the same rate. A 100-connector cable (not too out there) could then use 4 kW. That's my guess, anyway.

There's probably some old dogs around here who have experience with these things - I'm curious to know too. :)

I do love the data sheet for it... Viewing Angle: 12 o'clock. Say what? :)

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4000W is a typographical error

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If this is a one-off, another option is to get a more expensive display which is already mounted, like-
http://store.gravitech.us/2tftco...

There is probably a bunch more on ebay also, but most will likely come directly from China (I guess you would just be eliminating the middleman, as everything comes from China anyhow).

http://www.mtcnet.net/~henryvm/a...

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Thanks for the feedback, everyone.

With the eBay pricing I could probably buy a bunch and keep trying until I get the flex tail soldering right!

The MTCNet link has some nice photos of the display. I particularly like the aircraft artificial horizon, complete with 3-D'd text, (2D, 3D..., it is slanted, angled, and of decreasing size...). I think it was Bob G who had a thread about the optimal algorithm to fill in the partial circle interiors for just such a project!

I'd still prefer to solder my own, rather than use a "breakout" board, but only if it is feasible to do so...

JC

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DocJC wrote:
I am looking at several GLCD's for a one-off project, and Crystalfontz has quite a selection, such as this one: 240x320 RGB, 8-bit interface, 3V .

The description states it has a "flex tail" and is designed to be soldered to PCB pads using a "hot-bar" soldering machine.

Question is this: Can I hand solder this to a PCB using my "normal' soldering iron that I use for through hole and SMD PCB soldering :?:

Yes.
Via google "hot bar" site:crystalfontz.com
http://www.crystalfontz.com/forum/showthread.php?t=6301
1. A possibility is solder mask, solder paste lightly by hand or better by an inexpensive stencil, kapton tape to hold tab onto PCB, hot air pre-heat from below and low flow hot air from above.
2. "CHIP QUIK" melts at 136F/58C; if its conductive enough then that will not melt the tab but won't work for desert environs ;-)
3. Temperature-controlled iron and paste flux.
4. Schmartboard may make an adapter for it:
http://www.schmartboard.com/index.asp?page=products_connectors
Schmartboard is doing a SMT connector survey.
"selection" - more at: http://www.newhavendisplay.com/
edit: #2 revised.

"Dare to be naïve." - Buckminster Fuller

Last Edited: Tue. Sep 14, 2010 - 06:54 AM
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gchapman,

Thanks for the link to the CF forum, and this particular thread!

I like the list of options you have outlined above, but I like even better the fact that at least two of the posters stated that they have hand soldered the flex tail connector.

There is light at the end of the tunnel. One more hurdle seems to be resolvable.

JC

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Shortly I'll be having a go at hot-bar connectors with one of the TFTs from Newhaven Display. They have a small amount of discussion about it on their forums, I'm optimistic that it should be possible with a regular iron and a good PCB footprint.

Of course I could also be proven horribly wrong...

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I am looking forward to hearing your results with both a hot-bar soldering station, and with a soldering iron. A photo or two of the hot-bar station would be nice, and of the results of both systems!

I hope all goes well for you!

JC

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My limited experience with this style of thing is due to the solder bumps, this creates a gap so to solder each connection, you need to press down with the soldering iron, this tends to damage the substrate. A hot air tool might work but the hot bar obviously heats all connections at once and avoids the problem.

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Quote:
you need to press down with the soldering iron

What I was contemplating trying was tinning the pads in a manner such I as do for SMD soldering, then pressing down on the Flex-Tail with a pencil eraser, while heating the PCB trace to reflow the tinned pad. Then repeat a bunch more times.

Perhaps it won't be difficult at all, but I wanted to hear from others before I decided how many displays to purchase, (one or two , perhaps even ZERO, if it sounded impractical to manually solder them, a few more otherwise).

(By the time I hack out a driver for the display, it would be nice to be able to use it for several projects!)

JC

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I was able to hand solder this one

http://www.crystalfontz.com/prod...

it is probably very similar to the one you are looking at. I did it by hand with just an iron, not too hard, looked like a shitty solder job but it worked.

With the contacts on the tail facing up, I just put a good amount of solder on each contact, the solder flows over the edge of the contacts and makes it way to the PCB pads.

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Uploaded with ImageShack.us[img]

Never ended up using a QVGA display in my projects, after I prototyped the display and got it to display different shades of color, I realized how much horsepower was required to do anything practical with it.

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Hi Alan,

Quote:
I realized how much horsepower was required to do anything practical with it.

Sounds like a good reason for me to use an ARM. Now, if only BASCOM supported ARMs :cry:

Thank you for the further encouragement!

JC

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Not only computational HP, but you will probably need to add external ram.

I decided to put a webserver on my project and use a tablet/pc/cell phone as a display.

The CF displays are nicely priced, if I had to pick a TFT module it would be theirs.

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I think a connector like this one:

http://search.digikey.com/script...

should save you a lot of soldering grief. Hard to say since there is no pitch or total width specified in the drawings from the screen. All I know is I used one of these (more pins) to connect a 4.6in 24-bit TFT to an AVR32 about a year ago, and it fitted perfectly. The only difference I can note with your display's connector is yours has that extra material each side of the contacts, with the fixation holes. My guess is it can probably be cut off to fit almost any ZIF connector with the right pitch...

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http://www.lcd-module.com/produc...

Serial data and a wide PDIP construction.

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Quote:
you will probably need to add external ram

Hi Alan,
Yes, agreed. I am not planning on using video for this project, which makes things much simpler. I was thinking of adding a FRAM chip for a video screen buffer, (or two...).

Hugo,
Cool. I'm still in the design stage, and looking at the "major hurdles" I need to conquer, and had not yet even looked for or considered a flex connector instead of direct soldering. I appreciate the link, and it opens up some options for me to consider further.

TVI,
Nice displays, SPI & I2C interfaces, touch screen options. Lots to look at, and Mouser as a USA supplier. Thanks for the link.

JC

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If you are going to use a QVGA graphics module. Instead of starting with the module first, find an ARM Eval kit with a built in QVGA screen. Then try to find another screen that uses a similar driver that the ARM graphics libraries supports.

To do anything reasonably nice looking, you will probably need to rely heavily on the graphics library for the ARM you are using. Alternatively you can brew you own graphics libraries, but that alone can take an eternity.

Forget about I2C and SPI, they are dog slow when dealing with the huge amounts of data you need to move for QVGA resolution.

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Hi Alan,

I agree totally, but fortunately I am not looking for High, or even Medium level throughput.
I'd use an Arm if I knew C, but I don't, so I'm stuck for now, but an XMega should be fine.
I'll write my own driver as there are not a lot of Bascom color GLCD drivers out there.
Since I'm not looking for high throughput even my own bit-banged parallel interface or SPI'd driver should be fine.

Time will tell, but it is good to have a few projects that push one's current knowledge base!

JC

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If you need a 3.5" 320x240 dots TFT LCD module with Touch Panel and LCD controller, a model is recommanded to you: kitronix display K350QVG-V1-F. It has 8-bit/ 16-bit 8080 system interface, SPI or parallel interface, and it can be used in the following MCUs TI (Cortex-M3 ARM), Atmel AVR, STM32, LPC177X etc.
For example, it is used in TI/ Luminary Micro's reference design kits: RDK-IDM-SBC and RDK-IDM-L35,you can find them at the website:(
http://www.luminarymicro.com/pro...
and
http://www.luminarymicro.com/pro...)
There is rich hardware and software information about the TFT LCD module at the website, which can speed up your R&D process.
For more information about the module, please look:
http://www.ecplaza.net/product/2...

With best regards!
Jacky Sheng
E-mail: jacky_sheng@kitronix.com

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For a one-off this is ridiculous, but I still wonder if you could rig something up to do the hot bar soldering. Machine a 'tip' that would contact all traces at once and fits in a drill press chuck, with ~10cm extra length for heat transfer buffering. Line up the chuck and your PCB & flex tail with a test run, then heat up the 'tip' with a butane torch. Could use an infrared thermometer to make sure it's in the correct range, then press it down for 15-30 seconds...
Those hot bar machines look expensive, but extremely accurate, like those nano-precision photolithography exposure rigs.

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Thanks for the link, Jacky.

It would be helpful, for myself and perhaps others, if the web page with the description included a link to a full data sheet for the display.

JC