High density composite focal plane array
A composite focal plane assembly with an expandable architecture has a multi-layer, double-sided aluminum nitride (AlN) substrate and vertical architecture to achieve the dual function of focal plane and electronics backplane. Imaging dice and other electrical components are mounted and wire bonded to one surface and then direct backplane connectivity is provided on the opposing surface through a matrix of electrical contacts. In one embodiment, a flexible connector is sandwiched between the AlN focal plane and a FR-4 backplane is used to compensate for differences in coefficient of thermal expansion (CTE) between the AlN and commercially available high density circuit card connectors that are commonly manufactured from materials with CTE properties more closely approximating FR-4. In an alternate embodiment, the FR-4 and flexible connectors are eliminated by using high density circuit card connectors that are fabricated out of materials more closely matching the CTE of AlN.
1. A high-density composite focal plane array with an integral back plane comprising in combination:
an optically flat imaging plane board having vias through the thickness of the board and having at least one array of contacts on a back surface;
an array of imaging die on the optically flat imaging plane;
a back plane motherboard constructed of a material having a different coefficient of thermal expansion than that of the imaging plane board; and
a flexible connector array between the imaging plane board back surface and the motherboard.
2. The apparatus of claim 1 wherein the flexible connector array comprises solderless flexible connectors between the imaging plane board back surface and the motherboard.
3. The apparatus of claim 1 further comprising wire bond connections connecting the imaging die to the vias of the imaging plane board.
4. The apparatus of claim 1 further comprising vias, which are constructed in layers of the imaging plane board, wherein the vias provide a transition from wire bond patterns on the imaging plane to a back surface array, which matches the flexible connector array.
5. The apparatus of claim 1 wherein the imaging board is an aluminum nitrite board.
6. The apparatus of claim 1 wherein the motherboard is an FR-4 board.
7. The apparatus of claim 1 wherein the number of vias is substantially greater than the number of vias, which can be placed on a perimeter of the imaging plane board.
8. A high-density composite focal plane array with an integral back plane comprising in combination: an optically flat imaging plane board having vias through the thickness of the board and having at least one array of contact on a back surface; an array of imaging die on the optically flat imaging plane; a back plane motherboard constructed of a material having a coefficient of thermal expansion substantially matching that of the imaging plane board; and a connector array between the imaging plane board back surface and the motherboard.