The major key factor in a successful Reflow Oven build is modding the oven itself. So do make an effort to mod the oven in detail. You will be more than pleased with the results.
A general rule of thumb is that we want the highest heating power with the smallest allowable heating chamber. This way we can quickly ramp up the heat as required for reflowing.
For home electric ovens, we generally have two types of heating element to choose from. It's either Light-Based heating element or Tubular Metallic heating element.
Light-Based (IR / Quartz)
Light-based heating elements are fragile but heats up quickly.
There are two natural properties of light that we are most concerned with when reflowing: sensitivity to color and shadows.
Dark objects will heat up much faster; and where there is light, there is shadow. Shadows will reduce heat absorption.
If you must choose light-based elements. It would be desirable to look for milky white Quartz Elements with metal shielding. The metal shielding is necessary as it reduces direct light heating.
Do avoid clear tube IR.
The metallic heating elements heats up slower, but offers extended lifetime. It works by heating the air and transfers heat via hot air.
The advantage to using metallic elements is that it does not have the undesirable properties of light; consistency and stability should be much better for that reason.
There are generally two types of oven to choose from. Toaster Oven or Convection oven.
Toaster Oven's tend to be smaller and are usually equipped with quartz heating elements.
Since there is no fan to circulate the hot air around, toaster ovens are usually better suited for single side component placement as opposed to double side.
The toaster oven would work much like a hot plate; we'd like most heat to come from the bottom in such case.
Ovens with a circulation fan are typically referred to as a Convection Oven. They tend to be a bit larger than Toaster Ovens and are usually equipped with metallic heating elements.
Convection Fans give a tremendous added advantage of better heat distribution. It does so by circulating hot air inside the heating chamber. This will allow for better reflow of components on the reverse side.
One will need heat reflective material and also heat resistant tapes when modding the oven. There are several choices to consider.
The Reflect-A-Gold works as both a reflector and as a tape. Many have used it and the feedback is good. It is very easy to apply. Pretty much just tape and forget. It offers excellent reflective capability and do not peel off at high temperature.
It does emit some smell at high temperatures.
For some people this could be a very expensive commodity, so that means moving on to alternatives.
Kitchen Tin Foil
This is the low cost alternative that's also very easy to obtain. As a heat reflector it works amazingly well.
The only thing to remember to do is to at least double fold it. It does not have adhesive backing so it will need heat resistant tapes.
HEAT RESISTANT TAPES
Heat Resistant Tapes are often necessary to hold materials in place. They usually are not particularly good at reflecting heat. But they can endure heat.
Kapton tapes works quite well even at high temperature. No peeling is observed and no strange smell is produced.
Teflon Tapes works quite well also at high temperatures. It is much thicker than Kapton tapes and is more resistant to tearing and shearing than the Kapton tapes.
No peeling is observed and no strange smell is produced.
Aluminum Tapes offers excellent reflective capability. But unfortunately the ones used would peel off at high temperatures. In addition, there is a bit of strange smell at high temperature.
ADDING MORE HEAT
This is certainly something to consider. Often times, the stock oven just do not heat fast enough to achieve good reflow. In such case, we would need to increase the heating power.
But than the question becomes, do we want more top heating or more bottom heating? There is no right answer, it all depends.
The general rules of thumb are:
- Convection Oven: Top heating is more desirable. So if necessary more heating should be added to the top.
- Toaster Ovens: There is not a convection fan. So than bottom heating is more important. That means, additional elements should be added to the bottom.