Soldering liquid for SMD soldering using hot air
Opened this issue · 12 comments
Looking for recommendations with preference for chemical composition to make it myself.
Currently i have a custom solution using in short zinc dissolved in acid that is then neutralized and mixed with water set to evaporate at 280C.
The issue with it is that it leaves zinc residue behind.
NOTE: This also requires a constant flow of the liquid and doesn't transfer the heat efficiently enough (takes around 5 seconds to melt the tin evenly)
Abstract
Economical substance applied directly on the component connection point (tin connection) and heated up with a hot air station expecting to melt the tin and distribute the heat evenly at temperature around 240C (and lower ideally).
Challenges
1. Reaction with other elements:
The liquid has to not react with following as that would damage the components
- tin (used to bind components together)
- fibreglass (used for printed circuit boards)
- plastic (used in various places)
- gold (plated on connection points)
- Aluminium (used for connectors and cooling)
- Steel (used for connectors)
- Copper (used to make electrical connection)
- FIXME(Krey): Substance used to give PCB the color and to protect the traces
2. Has to stay on the board to allow melting of tin.
Expected to be present at all times to melt the tin.
3. Thermal conductivity
Tin melts at 231.93°C this liquid is expected to distribute the heat evenly and ideally serve as a reservoir for the heat to allow the hot air to be set on as lowest temperature as possible.
4. Toxicity
- Can't be toxic to human skin (would be painful to handle even though i use gloves when i work with electronics, ideally i want to have just nylon finger tips to not leave finger prints)
- breathing hazard (can be placed next to a fume extractor as needed)
5. Electrical conductivity
Expected to not be thermally conductive to prevent shorts in case the soldering liquid was not removed cleanly (shorts in circuit boards will cause component damage)
Optionally this can be placed in a super sonic cleaner after the soldering.
6. Thermal sensitivity of PCBs
Some boards are thermally sensitive where they might have a copper plate below that heats the protective coating and evaporates it.
^ This is handled by using soldering liquid or a flux and using 250~320C hot air while distributing the heat evenly
Relevants
- IEEE presentation on soldering liquid https://ewh.ieee.org/soc/cpmt/presentations/cpmt1702a.pdf
- Whiskering in metals https://en.wikipedia.org/wiki/Whisker_(metallurgy)
Boards have two characteristic temperatures. Tg is the glass transition temperature, where the PCB gets "rubbery". After that temperature there should be no strain on the PCB and should not be kept at that temperature on operation and under strain.
The second temperature is the Decomposition Temperature (Td) that is not to be exceeded in any case.
On the actual issue of inventing a new solder composition, be careful. Here are the ones that are known and governed by standards. Be sure that it is not toxic. There are so many health issues that might arise from such chemicals, and many of them are not immediate.
Sn-2.0Ag-0.5Cu (SAC205)
Sn-2.5Ag-0.8Cu-0.5Sb
Sn-3.0Ag-0.5Cu (SAC305)
Sn-0.7Cu-0.05Ni
Sn-4.0Ag-0.5Cu (SAC405)
Sn-0.7Cu-0.05Ni + Ge (SN100C)
Sn-3.8Ag-0.9Cu (SAC387)
Sn- 58Bi
Sn-3.5Ag
Sn- 57Bi-1.0Ag
Sn-3.7Ag
Sn-0.3Ag-0.7Cu+Bi (SACX)
Sn-4.0Ag
Sn-0.3Ag-0.7Cu+Bi+Ni+Cr (SACX)
Sn2Ag0.5Cu+0.05Ni
Sn-1.0Ag-0.5Cu + 0.02Ti
SAC 305+0.05Ni+0.5In
Sn-1.0Ag-0.7Cu+0.1Ge
Sn-2.5Ag-0.5Cu+0.5Co
Sn-1.2Ag-0.5Cu+0.05Ni (LF35)
Sn-3.5Ag + 0.05-0.25La
Sn-1.0Ag-0.5Cu (SAC105)
Sn-0.7Cu
Sn-1.0Ag-0.1Cu+0.02Ni+0.05In
Sn-3.0Ag-0.5Cu + 0.019Ce
@mehmetalianil How do you figure out the Tg and Td from the PCB without damaging it? (would like to make method that prevents me to go beyond the Td e.g. thermal camera + software controlled hot air)
@mehmetalianil Also you mentioned a soldering composition where i am working on a soldering liquid (meant to be put on a PCB to help redistribute the heat evenly at low temperature not the solder atm)
So, a flux?
@mehmetalianil How do you figure out the Tg and Td from the PCB without damaging it? (would like to make method that prevents me to go beyond the Td e.g. thermal camera + software controlled hot air)
It is hard but standard ish FR4 is Tg150 Tg 130. Yd is even harder, lemme check.
So, a flux?
Ideally not a lux see Abstract in the OP
In short i use these syringes to apply the liquid directly on the connection points (possibly modified with a longer needle)
and then i want to apply sub melting temperature of tin worth of heat from a hot air station on the component to not even get to Tg expecting the liquid is serve as a reservoir for heat to redistribute it evenly and melt the tin without evaporating to do a cleaner and more idiot-proof job.
Td is 300 minimum.
Td is 300 minimum.
See https://github.com/kreyware/repairs/issues/1 some boards seems to have lower Td (assuming that i didn't hug up there as the temperature set was 250C and the board got 284C when the hot air malfunctioned).
Also notice the zinc residue around.
Comparison for the zinc:
By the way, there is a phenomenon called tin whiskering to check out. Add that your liquid should not grow whiskers to the requirements.
@mehmetalianil noted, but is it relevant to the soldering liquid? (i do not expect tin in this soldering liquid)
Oh, relevant with tin. In the post tin was mentioned, that is why.