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LOCTITE ABLESTIK ABP 8068TB is a silver-filled semi-sintering die attach adhesive designed for semiconductor packages with high thermal and electrical requirements. It is formulated with a more enhanced resin bleed control than its predecessor LOCTITE ABLESTIK ABP 8068TA and it is designed to replace Pb Solder in Power and Low noise amplifier (RF SiP) type consumer applications. It is also a great solution for VCSEL (Vertical Cavity Surface Emitting Lasers) attach for 3D sensors.
LOCTITE ABLESTIK ABP 8068TB is designed to provide high adhesion and low stress which are essential for the thermal and reliability performances of high end power packages. The thermal performance of this material is comparable to that of a solder paste product (>100 W/mK thermal conductivity). It passes MSL 2A and MSL3 tests
LOCTITE ABLESTIK ABP 8068TB is not compatible with bare copper but it works fine and provides good sintering with Ag or Au electroplated Cu, Ag and PPF leadframes. It is an ideal solution for dies that are smaller than 2x2 mm and it can be fast and easily processed with standard die attach equipment
LOCTITE ABLESTIK ABP 8068TB can be used for Screen printing. But what is the process and what should you be careful of?
We have found that it is easier to achieve good results with a metal stencil (50um thickness seems ideal), compared with screen printing with a mesh (which tends to give a lower thickness and a rougher surface to the adhesive). Laser cut stainless is OK for a quick feasibility study, but I would recommend electroformed Nickel for good quality , high volume manufacturing.
It might be caused by too hard stencil unable to make a perfect fit with the substrate, due to the surface morphology. Using a mesh screen with an emulsion backing would probably solve this, but bring other processing issues.
Those can be caused as the stencil separates from the substrate, pulling up the edges of the printed adhesive. This can be improved by polishing the stencil apertures. Lower viscosity ABP 8068TA may be also worth testing in parallel if you observe dimple effects (although 8068TA also has a high thixotropic index of 6 for dispensing purposes)
Aperture reduction needs to be established by DOE trials, as it depends on component size, stencil thickness and customers inspection requirements. Regarding cooling rate, we do not believe this is critical, but thermal shock should be avoided. Normal practice is to allow parts to cool fairly slowly in the oven until below about 70C (when they are safe to handle).
Those will depend on the design of the print pattern and the equipment used, but the following will be a good starting point: