I hear this all the time, “We only have three profiles used on our production floor.” Just what does that mean? For some it may mean, “We only have three different oven settings used on our production floor.” For others it may mean, “We only have three different kinds of solder paste used on our production floor.”
Let’s get our terms straight and put some definition to a few keywords used here:
- The graphical plot of temperature as a function of time, as measured by one or more thermocouples at points of interest on a PCB
- Act of gathering the temperature as a function of time data using profiling instruments
- Oven settings required to produce the desired profile: Zone temperature settings (Set points), Conveyor speed setting, Convection rate or flow settings, Etc.
As a matter of fact, given a specific solder paste, there is only ONE profile you need to worry about- the one needed by that paste to properly heat the solder paste to make a good metallic bond between components and the substrate (typically plated pads on a PCB), and that does not cause damage to the components. However, depending on the characteristics of each oven (I.e. number of zones, convection rate, conveyor speed, etc) and the thermal nature of the assembly (I.e. its component density, board thickness, etc), there will be different oven recipes needed to make that single profile happen. In other words, different ovens will require different recipes to produce the same profile on a given assembly. Or, different assemblies will require different recipes in a given oven. So if you are soldering many different assemblies in a variety of ovens, you will have many oven recipes on the factory floor, even though you are trying to achieve only ONE profile, this is because you are using the same solder paste on all assemblies.
In the profile graph above, BOTH the Profile and oven Recipe needed to make the profile happen on this assembly are illustrated.
The oven Recipe needed to produce the correct thermal Profile on an assembly is NOT the same thing as a Profile. Or, a Profile is not a Profile, when it is a Recipe. Don’t be fooled when you hear, “We only have three profiles used on our production floor.” Find out exactly what is meant by this.
And remember, Profiling the assembly in the oven in order to fine tune the Recipe which will solder the assembly to meet the Profile needs of the solder paste (and not damage components) is a vital step toward a good thermal quality management program.