Melting point of common plastics? in this case in headers - Page 1
Forum section: electronics / beginners

author: cdev
author_rank: Super Contributor
timestamp: September 22, 2017, 12:59:39 am
content: I screwed up soldering in a row of headers and I need to redo it, and there is no way I know of to move the entire row without preheating it. Luckily I now have a digital hot plate which is fairly new and I am still figuring out what optimal temperatures are for things.. It heats things up on a block of aluminum.(Edit: After a examination of the actual distance the row needs to move, I think Tomorokoshi. is almost certainly right, de-soldering the row with braid will probably be possible. So I'm going to try to remove and re-solder the off alignment row now (see pic below with wire-wrap template for reference to how much it was off, maybe 1.5 to 2 mm, not so much.)With any luck I should be able to redo it that way. Read down a few messages for a good tip from Ian M. to prevent this from happening again in the future.Preheating would likely be a mistake.----original post: no longer the battle plan at all----reason: too complicated, unlikely to work...Unfortunately plastic I am sure melts at a lower temperature than (leaded) solder and I have no idea what that temperature is.I just hate the smell of burning plastic..What is a safe temperature where the header plastic won't melt, so that then I can bring the solder up the rest of the way with my soldering iron and move the headers so they are at the right 90 degree angle quickly, before they melt from the soldering iron's heat?Headers are just the usual breakaway type.. these are yellow and came with (and are on) a presumably mostly ROHS STM32 board.There are a hell of a lot of pins I am going to need to heat up, all at pretty close to the same time.So far Ive been using it at 95 degrees C. Nothing has fallen off or melted at that temperature, so far.I guess thats where I will start with this.

author: rdl
author_rank: Super Contributor
timestamp: September 22, 2017, 02:36:42 am
content: Other than trial and error, I think it would be nearly impossible to know the melting point of the plastic. There are simply too many types in use and they vary greatly.Can you just pry off the plastic part and remove the pins individually? Most often they are just friction fit.

author: cdev
author_rank: Super Contributor
timestamp: September 22, 2017, 02:52:29 am
content: Do you mean "move" the pins individually (not remove)?because that might be possible, actually.(The row of headers is soldered downward. So the blue pill board can be plugged into another board and replaced if it fails for any reason)But the headers ended up at slightly the wrong angle. In the future I think I'll try to pick and use my crappiest breadboard as sort of a sacrificial breadboard to hold pins while I'm soldering.

author: Ian.M
author_rank: Super Contributor
timestamp: September 22, 2017, 03:43:31 am
content: You don't even want the melting point as many plastics start to decompose or permanently deform below their melting point, and thermosetting plastics don't melt at all, they just decompose.I don't think you are going to win this one - trying to adjust the header angle without a thermally insulated clamp holding all the pins inline just isn't going to work. The plastic part will be softened by the heat of soldering and will either break or distort. It will leave the pins at small random angles from their desired orientation and maybe skewed as well. Removing the plastic part will be as bad, because then you have to get every pin into very close alignment before you can refit it. If you totally desolder each pin you *may* be able to reassemble and reuse the header, but better figure on replacing it.Don't use a breadboard as a jig - they melt too easily and provide very little lateral support. Use a stack of perfboard with interference fit alignment pins in corner holes, then lightly superglue the edges (enough to bond the stack by capillary action, but not enough to block the holes.

author: cdev
author_rank: Super Contributor
timestamp: September 22, 2017, 03:53:33 am
content: Ian,Your answers are often very very good. This is an example, thank you.Quote from: Ian.M onTodayat 21:43:31

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2017, 04:58:19 am
content: Note that the melting point of plastic on SMD header connectors is different than the through-hole counter parts....SMD versions will survive baking at solder melting temperature.If you were to attempt this with a through-hole connector on the PCB, it will melt into a gooie blob.

author: Brumby
author_rank: Unknown
timestamp: September 22, 2017, 06:07:38 am
content: Quote from: cdev on September 22, 2017, 02:52:29 amIn the future, position the header in place and then solder ONE pin at one end. Check for orientation and, if it is not OK, you only have one pin to release in order to make an adjustment. When this is good, then solder ONE pin at the other end and double check. If something isn't quite right, then there is a maximum of two pins you need to deal with.Once the two end ones are done and everything looks OK, do a few more and make sure everything looks good before finishing it off.Trying to straighten them in place might work - but without knowing exactly how far off they are, it's kinda hard to say how effective or safe that might be.The other approach is - to ensure the PCB is not pushed over the edge, consider the header forfeit and do whatever you need to make removal of the soldered pins one by one possible. I did this with a 24 pin power connector on a PC motherboard - I carefully destroyed the plastic of the socket so I could desolder each pin separately - then I soldered in a replacement. This worked - and I go another 3 years out of that machine before it failed from other age-related problems.

author: rdl
author_rank: Super Contributor
timestamp: September 22, 2017, 03:00:44 pm
content: This is what I was talking about, removing the plastic part completely so that the pins could be desoldered individually. I suppose it would make it a bit easier to bend the pins back into alignment, but headers are pretty cheap - probably best to just replace it.Quote from: Brumby on September 22, 2017, 06:07:38 am

author: elecman14
author_rank: Unknown
timestamp: September 22, 2017, 03:30:48 pm
content: My advice is that if you source connectors and header from a source that can provide a data sheet you should get parameters like max temp, and a thermal profile. This coupled with some kapton tape and thermal couples you should be able to see if you are in the ball park for not destroying the parts during soldering.Also if you are looking into removing the part intact I would look into using desoldering needles.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: September 22, 2017, 03:37:50 pm
content: Use solder wick to remove the solder from each pin individually.When installing headers like that, install the mating connector first before soldering any pins. This keeps the pins aligned if the plastic heats up enough to lose strength.

author: cdev
author_rank: Super Contributor
timestamp: September 22, 2017, 04:34:57 pm
content: Quote from: cdev onYesterdayat 18:59:39