Trying to heat-test some Nitto and Chukoh PTFE adhesive tapes

How do you hold components in place while soldering? Not the PCBs on which the components are mounted. PCB holders and PCB vises can be pricey but are readily available if you want or need one. I mean the components themselves: ICs, resistors, capacitors, diodes, etc. I’m thinking primarily of through-hole components, because that’s what I’m usually soldering, but this can also apply to surface-mount parts.

Given my druthers, I’d always populate the board completely and then do all of the soldering in one go. Sometimes, however, that’s not feasible. With through-hole components, one solders with the PCB upside-down or at a mostly-downwards angle (components facing down, or outwards if the PCB is in a PCB vise). Most soldering tutorials I’ve seen suggest splaying the legs of through-hole parts before flipping the PCB over to solder and then snipping off the excess “leg” material with side-cutters.

The splayed-leg approach works, but can get hairy if there are many components close together. It’s also tough to keep parts flush against the PCB. They seem to inevitably end up protruding a millimeter or more above and may even have shifted a bit more on one leg than the other, so the result is often visibly less tidy than one might have preferred. Something also seems “off”, to me, about the asymmetric distribution of solder at the joint: comparatively little between the leg and the place along the annular ring of copper around its mounting hole at the point where the leg is pressed outwards and much more between the leg and the opposite side of the hole.

Holding components to a PCB with tape works. Depending on the type of component and the hole spacing, however, a decent amount of the metal of the part’s leg material may be exposed on the component-side of the board. That can get quite warm during soldering and, if the piece of tape you’re using to hold the part on the PCB is contacting that bit of metal, the tape is going to get hot as well. Additionally, non-leaded solders require even higher soldering iron tip temperatures than leaded solders. Regular transparent office-supply-closet types of adhesive tape will melt in such circumstances.

The first sort of high-temperature-tolerant tape that I used, some years back, to hold components in place during soldering was Kapton. They’ve never really worked very well for me. The Kapton tapes I’ve tried have seemed too rigid and/or their adhesive too weak to allow them to conform closely to parts and the boards I’ve used them on and lengths of Kapton tape springing up from the PCB has been a problem.

More recently, I’ve been employing some PTFE tapes with silicone adhesives: Nitto NITOFLON 973UL (fiberglass and PTFE), Nitto NITOFLON 903UL (PTFE only), and Chukoh AGF-100FR (fiberglass and PTFE). They’re only rated for use between -60°C and 200°C, however, whereas Kapton is good up to 400°C. I use exclusively non-leaded solder and usually have my iron set for 340°C. I’m not touching the component-side of the board with the iron’s tip, however, and definitely not directly contacting any of the tape. Nevertheless, heat conduction is a thing and, no matter how quickly I work, the tape is going to get hotter than ambient.

I’ve been using them for months without any obvious issues. I haven’t yet tried measuring the maximum temperatures to which they’re getting exposed in my use case, but I was curious to see what failure of these tapes would look like and whether they’d start to break down in some fashion before reaching their 200°C maximum, operating on the assumption that I’ve been quick and nimble enough in soldering that they’ve never yet gotten that hot for me.

My first experimental setup (in the photo immediately preceding this paragraph) featured an inverted aluminum jell-o mold. I used similar lengths of the three tapes to affix a thermocouple tip to the aluminum and weighted each piece of tape with a small stainless steel carriage bolt in hopes of observing slipping once the tapes heated up. The jell-o mold was elevated on a support stand, supported from below by one support ring, and held in place by a second support ring tightly pressed over the top.

My first heat source was a large candle placed with the flame below the center of the jell-o mold. The highest temperature reading I could get with the candle, for any of the three thermocouples, was slightly over 120°C. That was with the candle flame as close as far up inside the mold as it would go without going out.

Replacing the candle with a hand held heat gun of the sort used to help strip paint got the thermocouples readings into the 220s°C, but not at the same time. In the image above, a screen capture from video I took of my efforts, cropped to show the screen of the quad-thermocouple temperature sensor I used, the third thermocouple (the one beneath the PTFE-only Nitto tape) is reading near-ambient (like the fourth thermocouple, which I didn’t need and left coiled with its tip near the sensor casing) because the wire had been under a bit of tension and sprung free by that point. The Nitto 903UL tape itself, however, looked fine. None of the three types of tape had dropped their bolts or shown any hint of slippage. Afterwards, they peeled off readily and didn’t seem any the worse for wear.

The backwash of hot air from the inside of the jello-mold was hitting the hand holding the heat gun and that got uncomfortable quickly, but I wanted to go higher, temperature-wise. Once everything had cooled down, I swapped the jello-mold out for a small metal plate and gave it a second shot, with the thermocouple wires arranged better (and run through a small support ring) to reduce springiness. That’s the setup shown in the first couple of photos in this post.

Unfortunately, the plate setup was less effective than the jell-o mold version. I wasn’t able to get any of the thermocouples to read very much over 200°C. Moreover, the highest values were only achieved for the center-tape thermocouple. The ones on either side, particularly the one closest to the metal clamp holding it to the support stand upright, didn’t get nearly as hot. The heat was being radiated away and conducted away via the clamp. Temperature-wise, the mold had done a better job of capturing heat and had heated up more uniformly. The shape had likely played a part in that, as well as the fact that the ring supports I used to hold the mold in place were coated with silicone or something similarly less heat-conductive than bare metal would’ve been.

In this second iteration, two bolts (hanging directly downwards rather than resting against the curved dome of the mold) were released. The Nitto 903UL bolt dropped first, followed some time later by the Chukoh AGF-100FR bolt. All three pieces of tape peeled off easily, weren’t noticeably damaged by the heating, and (as before) left no obvious adhesive residue behind.

This wasn’t a very rigorous experiment, but the first iteration, with the jell-o mold, has afforded me a small additional measure of confidence that these three tapes aren’t likely to spontaneously liquefy or combust immediately if they’re exposed to temperatures slightly in excess of their promised range.