Copper is a metal used widely as the 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. The 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 the oxidation barrier is
actively being researched.
< Surface images and TEM & EDS of Cu plates coated by
ALD thin films after annealing test >
After depositing Al2O3 layers on Cu-plated plates with
various film thicknesses and process temperatures, the oxidation and corrosion
behavior of the coated copper was examined with different annealing times in the 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 the case of 60 cycles and 100℃ after annealing for 24hr.
To analyze the change of the structure and confirm the oxidation
behavior, TEM and EDS were 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 the 5nm Al2O3 layer and outer oxygen after annealing.
On the other side, in the case of depositing 10nm Al2O3 film,
the ALD layer was maintained after annealing, so Cu oxide layer wasn’t built on the
surface. Therefore it confirmed that 10nm ALD Al2O3 layer showed an excellent
corrosion barrier.
< ALD equipment for Lead Frame and PCB >
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 application. ALD tools for Lead Frames could be
used by adding a 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 the new ALD application area continuously
through constant R&D.
Source:
http://www.ncdtech.co.kr/2018/bbs/board.php?bo_table=eng_board_05&wr_id=57