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< Surface images and TEM & EDS of Cu plates coated by ALD thin films after annealing test >
< ALD equipment for Lead Frame and PCB >
Copper is a metal used widely as main material of Printed Circuit Board (PCB) and Lead Frame. But it is required to protect the oxidation because copper is easily oxidized in the condition of humidity, temperature and pH, etc.
Electroless Nickel Immersion Gold (ENIG), Organic Solderability Preservative (OSP), Immersion Sn or Ag (ImSn or ImAg) is generally used to prevent oxidation of opened copper area after Solder Masking in PCBs. Lead Frame is protected from oxidizing by plating Au, Ag, Pd and Ni after Lead Frame forming.
Recently, many groups have studied about preventing oxidation on the surface of copper by various corrosion protection layers of ALD metal oxides. Especially, Appling Al2O3 layer to oxidation barrier is actively being researched.
After depositing Al2O3 layers on Cu plated plates with various film thicknesses and process temperatures, oxidation and corrosion behavior of the coated copper was examined with different annealing times in oven. There was no oxidation before annealing, but after annealing for 1hr, as the sample’s thickness lowered and process temperature decreased, the oxidation happened and increased gradually. There was no oxidation on the plates coated with 50~60 ALD cycles and at process temperatures of 70~100℃ after annealing for 5hr, and oxidation didn’t occur only in case of 60 cycles and 100℃ after annealing for 24hr.
To analyze change of the structure and confirm the oxidation behavior, TEM and EDS was measured on 5 and 10nm Al2O3 coated Cu plates at 100℃. The results showed that a thick Cu oxide layer was built by combining Cu coming out through 5nm Al2O3 layer and outer oxygen after annealing. On the other side, in case of depositing 10nm Al2O3 film, the ALD layer maintained after annealing so Cu oxide layer wasn’t built on the surface. Therefore it confirmed that 10nm ALD Al2O3 layer showed excellent corrosion barrier.
Copper based PCBs and Lead Frames for semiconductors may have great properties to prevent humidity and oxygen by ALD coated corrosion barriers.
NCD has high volume and large area ALD equipment and technology for this kind of applications. ALD tools for Lead Frames could be used by adding dedicated transfer module on the base of Lucida GSH Series. And NCD has been developing new ALD equipment, Lucida GP Series, for large and flexible PCB substrates. NCD would extend new ALD application area continuously through constant R&D. (revieced by YB)