A method for solid state bonding of a plurality of metallic layers and devices made by that method are disclosed. First and second metallic layers are solid state bonded utilizing a protective coating on the non-bonded surfaces that engage the pressure applying appliance to prevent the surfaces from adhering to the pressure applying appliance and to protect the surfaces from imprinting during the bonding process. The invention can be used to fabricate micro-channel devices with smooth outer surfaces and eliminate mold release compounds utilized in conventional bonding procedures.