Flip-chip mounting of optoelectronic chips
An optoelectronic assembly includes an integrated circuit (IC) chip including, on its front side, a photoconversion region and first electrical contact pads disposed alongside the photoconversion region. A circuit substrate contains a cavity into which the IC chip is inserted through the lower side and has a window opening through the upper side in communication with the cavity such that the photoconversion region of the IC chip is exposed through the window. The circuit substrate includes electrical circuit traces, which include second electrical contact pads disposed within the cavity alongside the window so as to contact the first electrical contact pads on the front side of the IC chip within the cavity. A base includes a stiff, heat-conducting material, to which the lower side of the circuit substrate is fixed. A malleable heat-conducting layer is compressed between the rear side of the IC chip and the base.
1. An optoelectronic assembly, comprising:
an integrated circuit (IC) chip having front and rear sides, and comprising, on the front side, a photoconversion region and first electrical contact pads disposed alongside the photoconversion region;
a circuit substrate having upper and lower sides, and containing a cavity into which the IC chip is inserted through the lower side and having a window opening through the upper side in communication with the cavity such that the photoconversion region of the IC chip is exposed through the window, the circuit substrate comprising electrical circuit traces, which comprise second electrical contact pads disposed within the cavity alongside the window so as to contact the first electrical contact pads on the front side of the IC chip within the cavity;
a base comprising a stiff, heat-conducting material, to which the lower side of the circuit substrate is fixed; and
a malleable heat-conducting layer, which has a thermal conductivity of at least 1 watt/meter-kelvin and is compressed between the rear side of the IC chip and the base such that compression of the heat-conducting layer between the chip and the base reduces a thickness of the heat-conducting layer by at least 10% relative to an initial, uncompressed thickness of the heat-conducting layer.
2. The assembly according to claim 1 , wherein the IC chip comprises an image sensor, and the photoconversion region comprises a photodetector array.
3. The assembly according to claim 2 , and comprising a lens mounted over the circuit substrate and configured to form an optical image on the photodetector array.
4. The assembly according to claim 3 , and comprising an optical filter mounted over the window in the circuit substrate.
5. The assembly according to claim 1 , and comprising one or more electronic components mounted on the upper side of the circuit substrate in contact with the electrical circuit traces.
6. The assembly according to claim 1 , and comprising a printed circuit, which is overlaid on the base and comprises electrical connections that make contact with the electrical circuit traces on the circuit substrate.
7. The assembly according to claim 1 , wherein the IC chip has a thickness between the front and rear sides of at least 0.2 mm.
8. The assembly according to claim 7 , wherein the thickness of the IC chip is at least 0.5 mm.
9. The assembly according to claim 7 , wherein the thickness of the IC chip is within ±0.1 mm of a depth of the cavity in the circuit substrate.
10. The assembly according to claim 1 , wherein the heat-conducting layer comprises a thermal adhesive.
11. The assembly according to claim 1 , wherein the heat-conducting layer comprises a thermal gel.
12. The assembly according to claim 1 , wherein the heat-conducting layer comprises a thermal pad.