Nickel Plated Brass Frame Surface Modification And Emc Adhesion

As electronic devices were further developed, the reliability issues of package have attracted much more attention than before. Now in electronic packaging, plastic package and Cu based leadframes are mainstream. Delamination, often occurring at the interface of leadframe and epoxy molding compound (EMC) in plastic packages, often lead to popcorning during/after the solder reflow process due to the weak bonding at the interface, resulting in the cracking of the whole package. It's a common failure mold in package. The PPF (pre-plated frame) technology is used to improve the solderability. however, it results in a weak bonding between the EMC and the plating metals on leadframe. So the weak adhesion between leadframe and EMC causes more failure in plastic package. To enhance the adhesion, many researches focus on leadframe surface modification recently.Using O2,N2,CO,and CO2 as source gas, the Cu leadframes pre-plated with nickel were modified by Plasma Immersion Ion Implantation (PIII) technique. Optical microscope, scanning electron microscope (SEM), and atomic force microscope (AFM) were used to observe the morphology change caused by PHI treatment. However, the morphology didn't change obviously, for the leadframe surface had high roughness. The contact angle measurement was used to show the wettability of leadframe surface. PHI technology could enhance the wettability significantly, but it only last for a short time. And the wettability didn't influence the adhesion in packaging process. From the plasma optical emission spectroscopy analyses, we could know the components were implanted into leadframe during PHI treatment. CO and CO2 plasma optical emission spectroscopy showed that they have the same main components of exited CO molecule, CO+, CO2+, and CO had a higher density. X-ray Photoelectron Spectroscopy (XPS) was used to analysis the leadframe surface chemical state. The carbonyl was both observed by XPS on leadframes after CO and CO2 plasma implantation treatment. The pull test showed that, comparing with leadframes without treatment, the adhesion strength between the leadframe and epoxy molding compound (EMC) increased significantly after CO and CO2 plasma implantation, respectively. While after O2 and N2 plasma implantation the adhesion strength didn't change obviously. According to the leadframe surface analysis, the morphology and wettability didn't influence adhesion strength. It was carbonyl group induced by CO and CO2 plasma implantation treatment that formed chemical bond during packaging process and enhanced the adhesion strength dramatically. The mechanism of carbonyl enhancing the adhesion strength was discussed. After pull test, the leadframe surface was checked by SEM, and the EMC was found on the leadframe with CO and CO2 plasma implantation treatment. It also proved that chemical bond was formed between the leadframe and EMC.Thermal technology was applied to modify the leadframe surface, using CO and CH4 as reaction gases. XPS was used to analysis the leadframe surface chemical state. The pull test showed that adhesion strength between the leadframe and EMC increased obviously when the reaction temperature at 60℃for both gases. But at 100℃, the effect of CO thermal treatment declined. The mechanisms of enhancing adhesion strength were discussed. For CO thermal treatment, it was carbonyl appeared on leadframe surface that enhancing adhesion strength. And the carbonyl formation was discussed. While for the CH4, it was carbonyl, methoxy or both that affected the leadframe surface chemical state.