Proper Soldering Technique
Soldering is something nearly everybody in the CRL is going to need to do, at some point. Good soldering is about getting
the right amount of heat and the right amount of flux with the right amount of solder.
Basic steps:
- 1. Pre-tin the wire.
- 2. Pre-tin the contact.
- 3. Bring the wire and contact together and melt the solders together. (Add more solder if needed. The solder contains a core of flux to help clean the metals and make them flow better.)
Soldering is all about getting the right level of heat between both metals that are being joined. Surface tension does all the work by "pulling" the solder into very close contact with all the metal surfaces. It must be clean to do this, because metal oxides prevent surface tension from doing its job. But heat produces metal oxides! So, we use flux to clean away the oxides. Flux is included in the core of most wire solders and we also have little containers of various kinds of flux paste in the lab. Flux is absolutely critical, because oxides occur very quickly at elevated temperatures!! You CANNOT get a good solder joint without flux!!
1. By "pre-tinning" I mean coat the bare wire with solder prior to connecting the two contacts together. Do this by stripping the necessary amount of insulation off of the wire to permit the connection. (This should be minimized. Keep the section of exposed wire as short as possible for the particular connection you are trying to achieve.) Next, with a clean, hot solder tip, apply heat to the bare wire. Then, touch the solder to the hot wire to melt it onto the wire. Surface tension should pull a nice amount of solder to the wire to coat it. (No need to overdue it with too much solder -- you want a nice complete coating.)
2. Do the same to the contact to which you want to connect: apply heat, then apply solder. (Use the metal to melt the solder, not the soldering iron. That lets you know it is hot enough.)
Tips:
- To help get the heat flowing, touch the end of the solder to the interface between the iron tip and the wire. A little melt will increase surface area and promote better heat transfer.
Using the Soldering Oven
The CRL has a Puhui infrared soldering oven.
Press "F4" for the English Menu and press "F3" to select a temperature profile. Several stored profiles are
available for different soldering chemistries. If you want to develop your own temperature profile, use wave 7 or 8
which can be customized to your needs.
Note that this oven is NOT a typical "set and forget" oven. The temperature can only cycle over a limited range for a limited cycle of only a few minutes.
Consult the user manual for detailed programming directions.
Basic steps:
- 1. Press F3 to select a temperature wave (profile).
- 2. Press F1/F2 to select wave 7 or wave 8 for a custom profile.
- 3. Press F3 to edit the time/temp parameters.
- 3. Press S to edit, then F1/F2 to select a time. Press F3/F4 to adjust the temp. Press S to save.
- 3. Press F4 to confirm selection.
Proper Wire Crimping Technique
We have a number of different types of connectors we use in the lab. Some require soldering, some require crimping with a special tool. IDC types (insulation-displacement connectors) do not
require stripping before the crimp, but do require a special crimping tool. Non-IDC connectors require the wire to be stripped before crimping.
Many of the crimping tools for connectors in the lab have a double set of teeth (as is often the case):
With these connectors, it is important that one set of teeth captures the insulation and one set of teeth captures the bare wire. We have many such crimp connectors and I want to make sure everybody knows how to use them properly to make good connections. Here is an image of a good crimp:
Stripping off the proper length of insulation from the proper size wire are important first steps. The picoblade connectors for the RecoNode are tiny and hard to handle! I generally place the female connector in the "B" slot of the crimp tool:
(The double teeth are indicated by the circle and the female connector is placed at the arrow.)
Then close the crimper most of the way (leaving some room for the wire):
Strip off a tiny length of insulation and slide it in and crimp until the ratchet stops and releases.
This captures the wire for a good electrical connection and the insulation for good mechanical strength. Don't be afraid to pull on the connector to make sure it is firmly attached. Don't worry if it pops off. Better to find out it is weak now than when you need it to work later on.
The crimp job above is using a bit too large of a piece of wire. (The insulation is straining too much.) The Molex crimper (red handle) notes the proper wire size is 28 to 32 gauge, stranded wire. (Always try to use stranded wire for crimp connectors.)
Check out :
Here is another link on single-tooth crimping :
Sparkfun single-tooth crimp notes
It is likely that everyone will need to do this at some point (PhD, MS or ugrad). Here is a bad example of a crimp that passes the "pull test" but will not do well in the long run:
Since the insulation (which doubles as a structural component) is not captured by the crimp, it does not relieve strain on the metal conductor. This type of crimp will work for awhile, but will eventually fail because the strain relief is not sufficient to protect the wire at the core. (Metal wire fatigues and breaks more easily than plastic insulation.) The point of crimping both the insulation and the wire conductor is to eliminate relative motion between the insulation and the terminal, preventing the wire from bending. As indicated in the photo, motion of the terminal will cause the wire to bend and eventually break. Not so for the previous picture above, which shows the insulation captured by the insulation crimp.
rvoyles [at] purdue [dot] edu
Purdue University, West Lafayette, IN 47907, (765) 494-4600