Best Way to Connect 16x2 LCD to SMD Board - Advice, Please.

[Resistoid]

Hello People,

I am looking for some advice on the best way to connect a 16x2 LCD screen to an SMD circuit board for mass production.

I have designed such a board with all components on the top side.

The 16x2 LCD is also supposed to sit flat on the top side of the board. The LCD's connections to the circuit board can be permanent (in normal operation there should be no need for the user to disconnect it).

At this point, I plan to house the completed boards in plastic cases with cut-outs for the LCD, buttons and external connections.

I have already tried surface-mount header pins; unfortunately the plastic block used to hold the pins in rows was taller than the space between the underside of the LCD and the top surface of the circuit board, so that didn't really work.

My questions:

1) What is the most cost-effective means for connecting the LCD screen to the circuit board in a mass production setting?

2) How are such screens connected normally in mass production? (- I couldn't find anything at home with such a screen to dismantle and investigate myself).

Thanks in advance.

Resistoid.

[mariush]

For mass production you would custom order lcd screens to fit a particular shape you need.

One option is for your box that holds everything would have plastic raised in the places where holes are in the corner of the lcd panel, to screw the lcd screen with self tap screws to the case and connect the screen to the board with wires or 0.1" pins
Another option would be... for connection, use 0.1" male header and female header to make the connection between the lcd screen and circuit board, or just use plain flat ribbon cable. If you use the 0.1" headers you already have a strong connection but it wouldn't hurt to lock the screen in place in the opposite corner or in several corners.

You ca use 1, 2 or 4 round or hex shaped spacers to get the lcd screen to a particular height... which look like these:

http://www.digikey.com/product-detail/en/V6622K/AE10789-ND/3511432
http://www.digikey.com/product-detail/en/V6622F/AE10791-ND/3511426
http://www.digikey.com/product-detail/en/V6622C/AE10793-ND/3511505
http://www.digikey.com/product-detail/en/24431/24431K-ND/1532163

There's all kinds of spacers, with smaller or longer screw (if you get the right length you could just straight solder them on the bottom side of the board)
Even one would probably be enough to keep the lcd screen in place, two will 100% keep it, four would be over the top and perfect.
There's also nylon spacers which are cheaper..

Here's a youtube video Dave has with a Turnigy charger that has this 16x2 style screen :



It's only held in place by the top pins which are soldered to the board.

In the same thread at the last page there's another teardown of such charger and you see there the screen is actually screwed to board with spacers like i described above :

https://www.eevblog.com/forum/blog/eevblog-397-turnigy-accucel-6-charger-teardown/msg200442/#msg200442

An inverter with custom 16x2 held in place by nylon spacers :

https://www.eevblog.com/forum/reviews/sma-sunny-boy-sb1700-solar-inverter/msg154810/#msg154810

[Resistoid]

Hello mariush.

- Thanks for your reply: You've obviously gone to a lot of trouble and it was very informative.

For anyone else able to reply, I should have made clear that it's really the electrical connections between LCD module and circuit board I am concerned about.

For the first few units at least I intend to use off-the-shelf parts wherever possible since this may be the less expensive way to get started.

The way my board is designed currently requires that the highest point on its surface should be the buttons since these ought to protrude beyond the surface of the case. Everything else including the LCD module should be lower. - That's why the LCD sits flat on the circuit board.

I've already tried the 0.1" male header pins you mentioned (soldered to board and then direct to LCD), but as you know, they didn't allow the board to sit flat. Female header sockets were avoided to keep the LCD as low and close to the board as possible. I suppose I could use the flat cable you suggested or add some caps to the buttons to make them "taller".

As you can tell probably, I aim to have as much of the production as possible automated to lower my start-up costs: (This was recommended in one of the tutorials Dave produced about "Design for Manufacture").

I expect that the flat cable would have to be soldered by hand at both ends, whereas SMD header pins can be positioned by the pick-and-place machine.

Am I right in thinking that the electrical connections on the LCD would have to be hand-soldered regardless of using pins or cable?

Thanks again.

Resistoid.

[notsob]

have a look at this sharp memory LCD, one version of it uses it uses a zebra 'elastomeric' connector, as the memory LCDs are probably too expensive for your project, try and find a 16 x 2 that uses a zebra strip for connection (as used on a few multimeters)

Cheers

Peter

[notsob]

here's a bit more on a zebra connector strip

http://www.fujipoly.com/products/zebra-elastomeric-connectors.html

[mariush]

I assume you have the kind of LCD screen that has all pins in a single line.

You know, there are lcd screens that have the pins in a 2x8 arrangement :

http://uk.farnell.com/midas/mc21605b6w-fptlw/lcd-2x16-fstn-white-led-b-l-5v/dp/2063169
http://uk.farnell.com/midas/mc21605b6w-spr/lcd-2x16-stn-reflective-5mm/dp/2063239

The size is pretty much standardized, they take about the same space and the holes on the side are almost if not exactly in the same place. You could actually make it possible to use both the in-line and 2x8 connection methods on the same pcb (so you could randomly use whatever lcd screens you get)

But anyway, the idea is that these that use 2x8 connectors are probably easier to mount.. Just put a 2x8 male header, a female header on the pcb and just press it down. Maybe use a spacer and screw on the other side just to be sure.

There are other screens which have a i2c connection, and apparently (at least the datasheet says so) they come with pins already on them but the holes are spaced differently, probably:

http://uk.farnell.com/midas/mccog21605d6w-sptlyi/lcd-cog-2x16-stn-grn-b-l-i2c/dp/2063205
http://uk.farnell.com/midas/mccog21605c6w-sptlyi/lcd-cog-2x16-stn-grn-b-l-i2c/dp/2063203
http://uk.farnell.com/midas/mccog21605c6w-bnmlwi/lcd-cog-2x16-neg-stn-w-b-l-i2c/dp/2063204
These may also be slimmer

There's also other screens on digikey.com made by newhaven  (search their site as well) - some of them i remember they had a type of flexstrip as connector so you could just surface mount the connector and slide the strip in the connector to get the connection.

On the buttons now.. are you sure you can't get tall buttons, there are buttons up to 15-20mm tall:

http://uk.farnell.com/multicomp/mc32867/switch-tactile-spst-no-50ma-thd/dp/1712982
http://uk.farnell.com/multicomp/mc32830/switch-tactile-spst-50ma-through/dp/1712953
http://uk.farnell.com/te-connectivity-alcoswitch/fsm8jh/switch-spst-0-05a-24vdc-pcb/dp/1555985
http://uk.farnell.com/alps/skhhbsa010/switch-tactile-6x6mm-vert-red/dp/2056814

See digikey and mouser as well, there's lots of buttons out there.

[Resistoid]

Hello Peter. - Thanks for the tips. I'd looked into elastomeric connectors briefly a few weeks ago and came away thinking they were suited primarily to making connections inside the LCD module. But now you mention some multimeters use them I think I'll re-investigate.

And you're right, the Sharp LCDs are very nice but way too expensive for this project: even the smallest one probably costs more than the total cost of an entire prototype of my design using the parts I've already selected!

Resistoid.

 

[Resistoid]

Hi mariush.

Thanks for the links.

I think I've pretty much found all the parts that will be used in the production version: Regarding performance, size and cost they fit the bill.

You're right, my LCD has 1x16 pins (using 4-bit communication and no backlight, so only 10 pins connected). Earlier prototypes used the 2x8 pin arrangement but for the reasons given above briefly I've settled on using a particular 1x16 from Winstar:

http://www.rapidonline.com/electronic-components/16x2-lcd-display-reflective-57-2224

I agree, though, it would be a very useful safeguard in production to be able to employ LCDs with different pin-arrangements just in case the supply of one sort dries up.

So far as I understand, switching from 4-bit to I2C would require a software re-write and at this point I've little inclination to do this since that part of the design has already been accomplished and works as planned.

When I carried out an extensive search for buttons last year I discovered that, as you say, there are many tall examples to be had in the 15-20mm range, but these are usually through-hole devices: My design is premised on using SMD parts wherever possible and keeping all components and soldering on one side of the board. By this means I hope to minimise human intervention.

15 - 20mm SMD tact switches are pretty hard to find at reasonable prices. Last year or the year before, I corresponded with a supplier who could get 20mm SMD tact switches, but he required a minimum order of about 1000 pieces, which was then impractical.

Eventually I got some suitable tact switches from Wurth which are about 13mm tall and that makes them the highest point on the circuit board in this prototype. My original SMD design had the LCD on spacers, as you mentioned, standing over other components. But this required much taller switches. It had the advantage of a smaller footprint so the FR4 circuit board cost would be lower per unit.

So, as things stand now, the only part of the project that seems to require hand soldering would be the connection of the header pins to the LCD module, or would that be automated too?

Resistoid.