Using Heat shrink tubing

Sorry if I'm sounding like I'm going from amateur to newbie but I have a question.

Today I bought heat shrink tubing in two sizes: 1/4 inch and 3/16 inch as those were the closest sizes to a 5mm LED.

First I tried the 3/16 inch tube and it fits completely over the LED except for the absolute bottom base part of it (which is about 1mm bigger in diameter). When I try the 1/4 inch tube, I can pass the entire LED inside of it.

The reason why I'm interested in tubing is because I have the LED about 2mm away from a very sensitive phototransistor and I do not want the phototransistor to be detected by the LED and I don't want to turn the LED off when its time for the phototransistor to detect remote lighting.

From what I understand, if I apply sufficient heat to the tube itself, it will shrink. This is desirable, however I don't want the top of the light hidden in the tubing, just the sides. Also, I do not want to damage parts due to excessive external heat.

So what is the absolute best way to make the heat shrink tubing super tight to the sides of the LED to the point where I can't easily pull it off and without damaging the LED or other nearby parts?

Run a clean, soldering fine tip soldering iron at low temperature along where you want it shrunk. Do it fast so the heatshrink doesn't melt. Don't use air.

It may also help if you stick a metal rod inside above the LED to brace the heatshrink from shrinking too much and it will also help absorb the heat in that area. Leave ample room to grip onto the rod so you can pull it out.

Also consider just gluing it on without applying heat, though you might want to use non-heatshrink material for this because they tend to be low-surface energy materials which are difficult to glue.

How about some plastic tubing from a biro for example?

What should I heat the tube with?

Use a standard hot air blower and trim after shrinking. If that doesn't work satisfactorily, I have used thin-wall aluminum tubing from a local hobby shop for shielding. You can also use black, PVC electrical tape.

I shrink heat shrink around LEDs all the time. This is Much Ado About Nothing to steal from Shakespeare. Hot air is the perfect right way to do it and you won't damage the LEDs. My experience with using the smaller diameter that won't go over the rim is that the heat shrink will slide off the LED. Use the larger size and position the end of the tubing before shrinking to expose the area you want. I used this technique to partially cover the dome of 3mm LEDs to adjust the size of the colon between 7 segment displays.

I use a hair drier to shrink tubing on to LEDs all the time & never had any problems.

A bread toaster works in a pinch too, for anyone without a hot air gun. It gives a much more even shrink than a soldering iron, and doesn't melt plastic onto the iron. (Just don't touch the elements with anything conductive)

"Embossing heat tools" can be had for about 15 bucks. Well worth the cost if you use much heat shrink. They are also can be used to remove surface mount components.

Hi,
When buying heat shrink, it sometimes shows the shrink rate, i,e, 2x, so if you bought 6mm it would shrink to 3mm. Make sure you have the correct one for your purpose.
Camerart.

Now, there is cold shrink tubing. https://www.digikey.com/catalog/en/partgroup/8420-series/2018?utm_adgroup=xGeneral Never used the stuff.

I was not really aware of that term used by JonSea. After a little research, I decided to get the Wagner HT400, which was a little more expensive then the generic others, was made in China like the rest, but had a lower DOA rate by reviewers. Got it today, and it works great for removing SMT devises. Maybe I was just lucky.

As background, I have a commercial heat gun (circa late 1960's) that will do anything, but its blast is a bit strong, a hobby heat gun (for shrinking polyester covering on model airplanes) , and a purpose-made plastic welder. Regarding the latter, it is great for its designed purpose, but a little too strong for a typical SMD. It does well for fully shielded and soldered RF devices.

Based on my very limited experience, I am quite satisfied with the Wagner tool for ordinary SMD. I am hoping it doesn't stop working in the next few weeks.

John