LED or semiconductor chip assembly processes typically use an electrically conductive, epoxy-based adhesive as a bonding agent. During thermal curing, low-viscosity components in the adhesive may flow out of the bond area and wet the surrounding surfaces, especially the electrical contacts for the wire bond pads. This phenomenon is known as 'bleeding'.
Adhesive bleeding weakens the connection between the contact wire and the wire bond pad. In the worst case the wire may lift, resulting in loss of electrical contact. Bleeding also has an adverse effect on the bond between the potting resin and the housing.
Working together with our partners, Plasmatreat has developed a special, ultra-thin nanocoating to address this problem. The PlasmaPlus® anti-bleeding coating prevents wetting of the contact surfaces and strengthens the wire connection, an added benefit which can be clearly demonstrated by wire-pull tests. The coating does not affect the bond between the adhesive and the lead frame. It is applied before chip bonding and remains extremely stable when stored under dry conditions.