Summary for post-bake timing Discussion
time requirements between plate and post-bake matter because hydrogen can become trapped under the plating and then diffuse deeper into the base metal as time passes. Doug Davis asked why a 4-hour post-bake might be less effective than an 8-hour or 23-hour bake, and James Watts explained that the sooner the part gets into the oven, the better: short delays let hydrogen move farther into the metal, making it harder to remove. Watts also noted that longer bake times can remove more of the deeper hydrogen, that plating thickness affects how easily hydrogen can escape, and that pickling or etching often contributes more surface hydrogen than plating itself. In a later question, Warren H. Anderson quoted ASTM B633 and asked whether the standard’s “within 4 hours after electroplating” means only one hour is available to reach temperature. The thread raises the timing issue but does not give a direct answer to that interpretation.
Q. Why is the time between plating and post-bake important? If a part receives a 4 hour post-bake instead of the 8 hr or 23 hr that may be required, what can be done? Why is the bake time sensitive?
Doug Davis
Project/Design Engineer – Tucson, Arizona, USA
2004
A. Because hydrogen is initially trapped between the plating layer and the parent metal. Over time, it diffuses into the metal, primarily along grain boundaries. The longer it is there, the deeper it goes into the metal. Baking is effective at removing the outer most hydrogen on/in the metal. It is less effective at removing deeper hydrogen. Thus, get it into the oven faster and limit your problems. The longer bake times will remove more of the deep hydrogen than a short bake time. Also note that the plating thickness has a great deal to do with the removal of the hydrogen as it must have a way to get out. Remember, that there is more hydrogen on/in the surface from the pickle or etch step than there is from the plating step in almost all situations. Please note that everything is relative. At what point does it become a serious problem.
James Watts
– Navarre, Florida
2004
2006
Q. ASTM B633, Section
6, Paragraph 6.6 states: “Œ..shall be baked at a minimum of
190 °C for 3 hours or more within 4 hours after electroplating to provide hydrogen embrittlement relief.”
Does this mean that there is only a one hour time window to get the plated part up to temperature in a bake oven?
Warren H. Anderson
– Elkhart, IN, USA