We are a contract manufacturer. We are constantly receiving MSD components in consignment kits that are not sealed, not in the right bags or have no desiccant. When this occurs, we bake the parts per JEDEC J-STD-033A. We recently received some parts from a customer that we had to bake previously for the last run. Is there a guideline that anyone is aware of that specifies the number of bake cycles allowed for a component?
Yes there is a limit to the bake cycles : "...the cumulative bake time at a temperature greater than 90C and up to 125C shall not exceed 48 hours. If the bake temprature is not greater than 90C, there is no limit on bake time..." Ref: J-STD-033A, section 188.8.131.52
As you are probably aware, the main concern with long bake cycles at higher temperature is related to lead oxidation and intermetallic growth that will degrade the component solderability.
If you take into account the MS level and body thickness you can sometimes reduce the duration of the bake cycle and therefore might be able to bake the same parts a few times at 125C. Of course when you have exceeded the 48 hours limit you can still bake at lower temperature if needed. The challenge is to find a way to keep track of this cumulative bake time if the parts are sent back and forth between you and your customer. You can contact me offline if you want more details on this subject.