Stacking multiple devices using single-piece interconnecting element
An embodiment of the present invention is a technique to stack multiple devices using an interconnecting element. A board has a periphery and top and bottom surfaces. The top surface has top contact pads to attach to a first device. The bottom surface is milled down to form a cavity confined by vertical walls around the periphery. The cavity fits a second device. Bottom contact pads are formed on bottom side of the vertical walls. The bottom contact pads are raised with respect to the bottom side of the vertical walls. Traces internal to the board connect the bottom contact pads to the top contact pads.
1. An interconnecting element comprising:
a board having a periphery and top and bottom surfaces, the top surface having top contact pads to attach to a first device, the bottom surface forming a cavity confined by vertical walls around the periphery, the cavity fitting a second device, the board attaching to the first device on the top surface and to the second device on the bottom surface in the cavity;
bottom contact pads formed on bottom side of the vertical walls, the bottom contact pads being raised with respect to the bottom side of the vertical walls; and
traces internal to the board to connect the bottom contact pads to the top contact pads.
2. The interconnecting element of claim 1 wherein the board comprises:
vias formed internally to connect the bottom contact pads and the top contact pads through the vertical walls.
3. The interconnecting element of claim 1 wherein the board comprises:
a metal plane between the top and bottom surfaces.
4. The interconnecting element of claim 1 further comprising:
an adhesive layer on the bottom surface in the cavity to attach to the second device.
5. The interconnecting element of claim 1 wherein the board is made of a flame retardant (FR) woven glass reinforced epoxy resin of type 4 (FR-4).
6. The interconnecting element of claim 1 wherein the top and bottom contact pads are made of copper.
7. The interconnecting element of claim 1 wherein at least one of the first and second devices is a ball grid array (BGA) device.
8. The interconnecting element of claim 1 wherein the adhesive layer provides control of co-planarity when the board is attached to a flat surface.
9. The interconnecting element of claim 1 wherein the bottom contact pads are formed within the bottom side of the vertical walls.
10. An assembly comprising:
first and second devices; and
an interconnecting element between the first and second devices, the interconnecting element comprising:
a first board having a periphery and first top and bottom surfaces, the first top surface having first top contact pads to attach to the first device, the first bottom surface forming a cavity confined by vertical walls around the periphery, the cavity fitting the second device, the first board attaching to the first device on the top surface and to the second device on the bottom surface in the cavity,
first bottom contact pads formed on bottom side of the vertical walls, the first bottom contact pads being raised with respect to the bottom side of the vertical walls, and
traces internal to the board to connect the first bottom contact pads to the first top contact pads.
11. The assembly of claim 10 wherein the first board comprises:
vias formed internally to connect the first bottom contact pads and the first top contact pads through the vertical walls.
12. The assembly of claim 10 wherein the first board comprises:
a metal plane between the first top and bottom surfaces.
13. The assembly of claim 10 wherein the interconnecting element further comprises:
an adhesive layer on the first bottom surface in the cavity to attach to the second device.
14. The assembly of claim 10 wherein the first board is made of a flame retardant (FR) woven glass reinforced epoxy resin of type 4 (FR-4).
15. The assembly of claim 10 wherein the first top and bottom contact pads are made of copper.
16. The assembly of claim 10 wherein at least one of the first and second devices is a ball grid array (BGA) device.
17. The assembly of claim 10 wherein the adhesive layer provides control of co-planarity when the first board is attached to a flat surface.
18. The assembly of claim 10 wherein the first bottom contact pads are formed within the bottom side of the vertical walls.
19. The assembly of claim 10 further comprising:
a second board having second top and bottom surfaces and internal traces, the second top surface having second top contact pads to attach to the first bottom contact pads of the interconnecting element and contacts of the second device, the second bottom surface having second contact pads to attach to a printed circuit board, the internal traces connecting the first bottom contact pads to the contacts of the second device.
20. The assembly of claim 19 wherein the second board has a size matched with size of the first board.
21. The assembly of claim 19 wherein the second contact pads match the contacts of one of the first and second devices.