I don't think the metal can makes much difference in this case, since it doesn't surround the bottom of the package. One IBM document says "A hard shell cover w

I don't think the metal can makes much difference in this case, since it doesn't surround the bottom of the package. One IBM document says "A hard shell cover was used to provide rugged external structure for handling purposes. Many different metals or plastics would suffice for this purpose. A stamped aluminum cap was chosen." In contrast, op amps and other precision analog components were often packaged in round metal cans, but these enclosed the IC on all sides. Ref: Page B-8 of http://bitsavers.org/pdf/ibm/logic/SLT_Circuit_Design_Hbk.pdf http://bitsavers.org/pdf/ibm/logic/SLT_Circuit_Design_Hbk.pd...