One of the challenges with scaling down this project is soldering the LCD. LCDs are commonly soldered to a PCB using through-hole technology because reflowing the entire LCD through an oven would damage it.

But given that I'm building a tiny PCB, I do not have a ton of room to do through-hole soldering: I needed this device to be on only one side of the PCD, i.e. SMD soldered.

Which brought up the question: could I damage the LCD by soldering so close to the glass?

I ran a quick test to see how much heat the LCD could handle before being damaged. The result: I could only *temporarily* damage the LCD after holding one of the pins at 300ºC for about 30 seconds. Any damage I could observed seemed to have disappeared after ~ 30 seconds.

So the takeaway: it's pretty safe to hold a hot soldering iron right up against the LCD glass while soldering, as long as it's for less than ~ 10 seconds or so. I could not see any noticeable damage at 5 seconds, for instance.

Results

I placed the soldering iron with solder on it right up against the corner of the pin where it touches the LCD glass.

And the soldering iron setting:

After each "test," I determined if the LCD was damaged by plugging it back into the device and running the display:

I did a variety of times. You can see what the LCD looks like when it has been damaged. It looks like some of the segments are faded.

In all instances, this damage appears to have been temporary. After 30 seconds, I could not see any fading like this again.