ATE PCBs can be up to 0.187-inch thick or even 0.25-inch, with a high layer count that includes a number of ground and power planes and have a lot of gold on the surface (typically 50 micro inches, ENIG) on the tester and DUT pads.
The size of the board along with the amount of metal it contains places major challenges on developing a profile and arriving at the ideal temperature. Consequently, developing the correct thermal profile for a test board is very different than that for a commercial 0.062 thick, 12, 14, or 16-layer board.
Due to the sheer number of internal layers, considerable heat is required to bring the board up to a temperature for the solder paste to reflow. It’s important that the heat profile is high enough for the paste to properly wet, but it is critical not to run too high a profile, which can damage the components or the board or both.
The challenge is to achieve the ideal temperature without burning the board or compromising the integrity of its various parts. Fig. 1 shows an example of data saved from a thermal profile. It is normally archived with a job’s history in case it needs to be referenced for future runs or to resolve issues.
Some things to consider when creating and defining a thermal profile:
- Type of solder paste being used
- Dimensions of the board (size and thickness)
- Layer stackup
- Type of components on the board
- Dielectric material
- Amount of metal on and in the board