LCD for handset and 3D printing help needed

[Mychaela Falconia]

Hello FreeCalypso community,

I've got a little bit of progress on the LCD selection front (finding
a suitable LCD module for our FC Libre Dumbphone handset), and I am
soliciting help from the community with getting a small 3D-printed
plastic part designed and produced.

After many weeks of delay I finally got the custom PCB which I created
for connecting HaoRan's HT020K1QC36S LCD to one of our FT2232D adapter
boards in the MCU host bus emulation mode, this custom LCD test board
has nothing but connectors and resistors on it, and last week I got
the needed help with populating it - I wasn't comfortable with
soldering the 0.5 mm pitch FPC connector myself, even with the use of
a good microscope at my day job - I couldn't tell if I was positioning
it correctly, and with such fine pitch it's very easy to move it off
the mark.  But I finally got it done with the help of my friends at
Technotronix, and was finally able to test this LCD.

Comparing the picture quality of this HaoRan LCD against the other LCD
for which I made the needed test rig a month and a half ago (Startek
KD020C-2A with special film modification), I got a surprising result:
the picture quality is almost exactly the same between the two, both
are very good, and the perception of one or the other being slightly
better is subjective.  I find this result surprising for two reasons:

* Startek's LCD is about double the price of HaoRan's, thus during all
of these many weeks of waiting I assumed that the cheaper LCD from
HaoRan would be inferior in quality - but it really isn't.  (And it is
not a Chinese vs. Western issue - both companies are in Shenzhen.)

* HaoRan's LCD is officially made for 6:00 viewing direction according
to both the datasheet and my communication with the vendor, whereas
Startek's LCD was originally a 12:00 display subsequently modified
with some special film for "free viewing angle".  Startek told me that
their film modification does not change it into a 6:00 display, yet
the way the two displays look from different angles is very much the
same.

So which are we going to use in our handset?  At first it would seem
that the choice is in favor of HaoRan because it's half the price for
the same picture quality, but then we've got mechanical mounting
considerations complicating the picture.  My overall plan for the
mechanical design of the handset as a whole calls for the LCD to be
mounted with its FPC tail folded under, so that the footprint of the
entire LCD arrangement projected onto the XY plane equals the
dimensions of just the LCD module itself, with *no* extra XY plane
space being taken up outside of this bounding box for the FPC tail or
the connector or any other extras.

But it appears that HaoRan's LCD was not designed at all for this FPC
folded-under arrangement, instead it appears to have been designed to
be used with its FPC tail stretched out.  If one were to mount this
LCD with its tail folded under, the contacts would end up facing
toward the top (toward the body of the LCD, not toward the PCB), and
there are no thin connectors for this unnatural contact direction,
only 2.0 mm tall ones.  As far as I can tell, the only sensible way to
use HaoRan's LCD with the mounting arrangement I seek would be to get
a custom modified version made with a solder-down tail; I asked Ivy
(HaoRan's saleslady) about it, and she said they can do it, but it
would require an MOQ of 1000 pcs, costing about $3200 USD - and I
would rather avoid this large MOQ and cost if we can.

If we were to use HaoRan's LCD as is and mount it with its tail
stretched out, there would be about 20 mm of dead space inserted
between the bottom of the LCD module and the top row of the keypad.
Look at a Pirelli DP-L10 phone and imagine how it would look and feel
if all of the keypad buttons were shifted downward by about 20 mm from
where they are now, leaving a giant dead space - not good at all.

But we may be able to do better with Startek's LCD if we can get a
custom plastic spacer produced in the needed small quantity by 3D
printing.  Yes, Startek's LCD is significantly more expensive in
absolute terms, but this cost would only matter in large quantities -
for the small quantity we need, the cost would be negligible.  Unlike
HaoRan's, this LCD has its tail contacts in the more natural
orientation (facing the bottom with the tail folded under), making it
easier to find a reasonably thin connector.  We also got some extra
luck with the pin count: Startek's tail has 45 pins (HaoRan's has 36),
and for this pin count I was able to find a thin connector (1.3 mm
height above the PCB) that officially accepts both straight and
tapered FPC ends, unlike Hirose FH33 series which is made in a wide
range of pin counts, but requires tapered FPC ends which the LCD
modules in question do not have.

So, what is this plastic spacer which we need to get designed and
3D-printed?  Look at the LCD mechanical drawing on page 6 of this
Startek datasheet:

https://www.freecalypso.org/members/falcon/lcd/KD020C-2A-XXX_SPEC_V1.0_1.pdf

The plastic spacer I envision would go between the LCD module and the
PCB, elevating the LCD above the PCB to make room for the connector
underneath.  The spacer would need to be in the shape of the Greek
capital letter Pi (same as Russian capital P), the width from the
outer edge of one leg to the outer edge of the other leg would need to
be 38.40 mm (the outer width of the LCD module), the length of each
leg would need to be about 41 mm, my current working target number for
the width of the "Pi" frame is 1.7 mm, and the thickness (the resulting
added height) needs to be 1.5 mm.

There is also one additional complication with the alignment pins.
There are two plastic pins (1.0 mm diameter, 0.85 mm long) protruding
from the back of the LCD module, meant to go into matching holes in the
PCB for alignment.  These plastic pins are located on the back of the
LCD module along the rim, thus the 3D-printed spacer would need to have
two matching holes for these pins to go into.  I am also considering
if we should put similar protruding pins of our own on the bottom of
our spacer piece, but I am undecided on this one.

Also as noted in the datasheet drawing, these LCD modules come with
very thin strips (it says 0.1 mm thickness) of double-sticky tape
along the outer vertical edges of the back of the module, covered with
protective film on delivery.  My plan is to have our spacer adhere to
the LCD module by way of this already-provided adhesive plus the two
alignment pins tightly fitting into perfectly matched holes in our
3D-printed piece, and then use another layer of adhesive (to be
selected much later) to stick the LCD+spacer assembly to the handset
prototype motherboard, so the resulting motherboard+LCD assembly will
be relatively solid without any case or enclosure to hold it together.

So, do we have anyone in our community who would be able and willing
to take on the challenge of designing and 3D-printing this plastic
spacer?

Hasta la Victoria, Siempre,
Mychaela aka The Mother