Im making a device and bought some arduino mini's and im wondering is it needed to be solded as the headers doesn't fit loosley. Also because i dont have the soldering iron in my possesion att he moment because i borrowed it out. Can i just use a gluegun to get them in place or will the metall have too much space inbetween?
Yes, anything supplied with separate header strips is intended to be soldered - the idea is you can solder other
things than the headers if you want, such as wires.
Well the thing is they fit pretty thight and the signal flows thorugh with out soldering them
Hi.
I have a pro mini here with unsoldered headers. It does feel the pins are making metal to metal contact with the pads. But...
Flaky joints are the biggest time waster in projects. It might seem the pins are making metal to metal contact but you'll never be sure the contacts are good enough. Many problems stop a project from working. Making all connections solid and robust eliminates a big source of trouble.
John.
The Pro Mini's I have holes larger than dupont header pins, unsurprizingly.
I stand by my posting. Glue gun is a hopeless idea! Solder them is the only way.
Your "need to solder" depends on your "need for reliability". If you just want to flash it, or run a quick experiment, sure why not? Beyond that, you are asking for trouble.
Such experiments must succeed. If not, you have no idea why they failed.
So the thing is, every so often on one or other of these fora, most often the "Displays" one, someone describes their problem with a project that does not work - such as one using a 1602 display with an I2C "backpack".
Suggestions go back and forth, the code is checked and seems to be correct after advice to use the "smart" library which automatically determines the display configuration. A picture of the arrangement is requested and examined and it suddenly becomes clear that the "backpack" or a header socket has not been soldered to the display.
OK, of recent times, we tend to short-circuit this time-waster and ask the question right at the start of the process. To those of us with any experience at all, the concept of needing to actually connect the parts together is so blindingly obvious that we can barely imagine it not being done as the first step.
But it appears that to a "newbie", this is not the case. 
If electronics is gong to be your hobby you need a soldering iron*.
I have something better now but for many years I used a cheap soldering irons similar to [u]this[/u]. (Radio Shack used to sell them for $1.99 or 2.99 USD and I went-through several of them.)
Of course you'll also need solder, and it's helpful to have some extra flux, plus some solder-wick and/or a solder sucker for cleaning-up & desoldering.
- You also need a muitimeter, and again, a cheap meter is better than no meter.
Solder... forget the commonly available lead free stuff. Look for a qualty brand like Ersin Multicore and 60:40 tin/lead alloy. Even those of us who have been soldering for 50 years hate the lead free junk.
On the contrary, use lead free and you don't have to worry about poisonous heavy metal contaimination.
But you must use the proper lead-free solder, that's the stuff with 4% silver. The stuff that's only tin and copper
is not usable as its not a eutectic alloy.
Anyone whose used the tin/copper stuff and thought that's what lead-free is like is missing out.
If you do use lead solder, 63/37 is the correct eutectic composition.
A eutectic melts and freezes as one phase, avoiding the pasty state that is difficult to work with.
Well Mark, we will have to agree to disagree! In my humble opinion, the only people who like lead free are those susceptible to the antics of Miss Grotty Thunderpants who want the active and efficient ingredients taken out of everything. You can't even buy decent paint stripper now (as an end user) for the same reasons.
Horses for courses.
"Poisonous heavy metal contamination" (spelling corrected) is a concern for manufacturers of electronic goods which will mostly end up in landfill and who-knows-where (fish!).
While your - our - projects and repairs may well in the fullness of time, end up in the same place, there are many orders of magnitude of difference. If you were going into bulk manufacturing of course you would need to be lead-free.