Semiconductor substrate having stress-absorbing surface layer
An assembly ( 101 ) comprising a semiconductor device ( 110 ) with solderable bumps ( 112 ); a substrate ( 120 ) with a layer ( 130 ) of a first insulating compound and an underlying metal layer ( 140 ) patterned in contact pads ( 141 ) and connecting traces ( 142 ), the insulating layer having openings ( 132 ) to expose the surface ( 142 a ) and sidewalls ( 142 b ) of underlying traces; the device bumps soldered onto the contact pads, establishing a gap ( 150 ) between device and top insulating layer; and a second insulating compound ( 160 ) cohesively filling the gap and the second openings, thereby touching the underlying traces, the second insulating compound having a higher glass transition temperature, a higher modulus, and a lower coefficient of thermal expansion than the first insulating compound.
1. A semiconductor flip-chip substrate assembly comprising:
a semiconductor device having terminals with solderable metal bumps;
a flat flip-chip substrate having a top layer of a first insulating compound and an underlying metal layer patterned in contact pads and connecting traces, the insulating layer having first openings to expose underlying contact pads and second openings to expose underlying connecting traces;
the semiconductor device assembled on the substrate wherein the device bumps are soldered through the first openings onto the contact pads, thereby establishing a gap between the device and the top insulating layer; and
a second insulating compound cohesively filling the gap and the second openings, thereby touching the underlying connecting traces, the second insulating compound having a higher glass transition temperature (T g ), a higher modulus, and a lower coefficient of thermal expansion (CTE) than the first insulating compound.
2. The assembly of claim 1 wherein the first insulating compound is a rigid polymer having a modulus typically in the range of 2 to 6 GPa at room temperature and a CTE in the range of 40 to 70 ppm/° C. below the glass transition temperature of the material, and the second insulating compound is an epoxy-based polymer containing an inorganic filler material and having a modulus typically in the range of 6 to 11 GPa at room temperature and a CTE in the range of 20 to 40 ppm/° C. below the glass transition temperature.
3. The assembly of claim 1 wherein the second openings expose the surface of the underlying connecting traces.
4. The assembly of claim 3 wherein the second openings include more than one opening for each connecting trace.
5. The assembly of claim 1 wherein the second openings expose the surface and the sidewalls of the underlying connecting traces.
6. The assembly of claim 1 wherein the semiconductor device is a semiconductor chip.