Abstract: In accordance with the present invention, it has been discovered that bias sputtering a metal layer (e.g., copper or aluminum) in an atmosphere of a mixture of ammonia and a noble gas leads to dramatically improved adhesion between deposited metal and a fluoropolymer substrate. Preferably, the bias sputtering takes place in an ammonia/argon gas mixture and most preferably in ammonia/argon gas mixture of 5 to 50 volume % ammonia and 50 to 95 volume % argon (most preferably 90/10 argon/ammonia). The use of an ammonia/noble gas atmosphere for bias sputtering is especially well suited for bias sputtering of copper seed layers onto fluoropolymer substrates. In general, the process for depositing a metal layer onto a surface of a fluoropolymer substrate in accordance with the present invention includes the steps of securing the fluoropolymer substrate to an electrically isolated conductive member (e.g.