Molding of devices and components is an important step in semiconductor packaging. The overmold protects the electronics from moisture, mechanical shock and vibration, and physical abuse. Good adhesion of the molding compound to the metal lead frame is a must.
Lead frames cleaned and activated with Surfx’s argon and oxygen plasmas exhibit higher bond strength to the molding compound. This is due to the large increase in surface free energy of the lead frames after treatment. Activation of the copper lead frames occurs at a scan speed of 25 to 50 millimeters per second. The copper does not change color during treatment, indicating that there is no significant oxidation of the metal.
Copper lead frames may be cleaned and activated using different plasma chemistries. A Cu strip was treated with argon plasma fed with 0.5% to 1.0% oxygen, nitrogen or hydrogen. After treatment, the surface free energy (SFE) was measured along with the polar and dispersive components of the SFE. These results are presented in the Figure below. Exposure to the argon and oxygen plasma increased the polar component of the surface free energy from <3 to 21 mN/m. Substantial increases in the polar component of the SFE were observed with the Ar-N2 and Ar-H2 plasmas, although to a lesser extent than with Ar-O2 plasma. A large increase in the polar component of the surface energy is a good indication that the copper lead frame is activated for bonding.
Surfx’s argon plasmas are easily integrated into molding machines. This is a fast, safe, and cost-effective way of activating metal lead frames for improved adhesion to the overmold. It eliminates handling and storage of lead frames, which reduces the risk of damage to high value semiconductor packages.