Using a home oven for solder paste

Question

I'm doing a project and I have a PCB which needs surface mount components attaching to it. One component has already been attached, and I have some 138deg solder paste in a syringe.

This is possibly going to sound very stupid, but is it feasible to use my kitchen oven or a similar household device to heat up the solder? This is just a one off for me and I am not planning on doing any surface mount soldering in future, and I do not have easy access to a proper reflow oven.

All the components will be mounted on one side if that's an issue.

Answer 1

Lots of people use toaster ovens and electric fry pans for reflow. It can get a little touch and go with lead-free solder, and I recommend leaded solder.

Large kitchen ovens likely don't have the oomph to bring things to temp fast enough, and your IC's may not tolerate the slow temperature profile.

I think whatever appliance you use, you should dedicate to reflow, and not use it for food.

Answer 2

Can you? Yes. Will it work every time... Maybe not!

There are two reasons for this.

1. Temperature profile and timing.

Reflow is done using two temperatures, a pre-soak temperature and a reflow temperature as shown below.

As such, you REALLY need to use two ovens to do this right, quickly switching it from one to the other after the pre-soak time.

2. Oxidation

Commercial reflow is usually done in a nitrogen gas so that oxidation will not occur in the solder and joints during the molten phase. That's rather hard to do in your domestic environment.

IN ADDITION:

Not all components can withstand the same heat. Some parts are MUCH more sensitive to being "cooked" for too long, especially plastic parts like connectors and the like. If you are doing this at home it is prudent to identify those and manually add them after.

SAFETY CONCERNS

Other than the obvious... "Don't burn yourself..." it is not a healthy idea to solder using the same oven you plan on baking that apple pie in later in the day. Lead and other noxious chemical fumes will permeate the oven.

Also, if you are married, severe tissue damage can occur in the rectal area from the insertion of your spouses footwear when she, or he, finds out what you did.

Answer 3

If you want to learn how to solder SMT components by hand in an unimpeachable fashion, I would recommend watching some of the Youtube videos by IPC (J-STD-001) certified soldering teachers. You will need pure IPA (isopropanol) not drugstore rubbing alcohol, cored solder in appropriate size(s), appropriate liquid flux and preferably a decent stereo microscope or at least a magnifier. And, of course, a clean well-lit work area, preferably with ESD precautions.

I would not recommend try to solder a one-off with solder paste. I do it myself with a stencil but the oven parameters are known-good for most boards. Even dispensing appropriate amounts of paste on each pad without a timed pneumatic dispenser is not easy (the solder paste behaves in a fairly unpleasant manner because it's not really a liquid- it's a bunch of little balls of solder in a matrix of liquid flux). Getting the oven right could result in damage to board. Sn63Pb37 leaded solder temperature-time profiles are relatively forgiving, but unleaded solder means running some parts very close to the point where damage occurs so the parameters have to be well controlled.

For something like a resistor you clean the board with IPA, maybe the part if it is not pristine, then tin one pad and slide the part in to solder one side, then solder the other pad. There are some subtleties as to where exactly you put the solder during the process- to get the part to wet, and then feeding it in at the junction of pad and part, while heating both with the iron. Then you clean and inspect and move on to the next. It takes a while but the results can be very good.

If you insist there are people who are successful using nothing more than a skillet but you will want to not use that for food afterward, especially if you are using lead-based solder. Make sure you wash your hands after handling the paste (as a paste it's worse than wire solder) and (if applicable) don't do it at all if there is any chance of pregnancy.

Answer 4

You probably wouldn't want to use a regular oven for three reasons:

1. Its probably not a good idea to put lead where food is.
2. A larger oven has more uneaven heating because there are more convection currents
3. The temperature profile of the solder paste would be hard to duplicate in a larger oven

Use a smaller toaster oven, get one from a second hand store. Look up the temperature profile for the paste you have, you need to time the temperature profile to that of the solder, you will get better results.

If this is just a one off PCB and you won't do it long term, find a cheap assembly place.

Another option is skipping the oven all together. A hot air rework station will probably do just fine in your case. There are numerous videos and tutorials on the web that show how to solder or use a hot air rework station with QFN's QFP's and other components. This is a good option if you have a low part count on the PCB or low quantity production run ~(<3 PCB's).

Answer 5

Please don't use microwave oven for the soldering techniques. The ovens that we use in home, is using the microwaves to get the heat. So you know the basics of microwaves and the semiconductor manufactures will strictly warn us about the ESD protection. So components may fail if you are using a microwave ovens. Instead use the IR ovens for the purpose. Maintain the temperature profile...enjoy