Plastic ball grid array package with integral heatsink
A plastic ball grid array semiconductor package employs a metal heat spreader having supporting arms embedded in the molding cap, in which the embedded supporting arms are not directly affixed to the substrate or in which any supporting arm that is affixed to the substrate is affixed using a resilient material such as an elastomeric adhesive. Also, a process for forming the package includes steps of placing the heat spreader in a mold cavity, placing the substrate over the mold cavity such that the die support surface of the substrate contacts the supporting arms of the heat spreader, and injecting the molding material into the cavity to form the molding cap. The substrate is positioned in register over the mold cavity such that as the molding material hardens to form the mold cap the embedded heat spreader becomes fixed in the appropriate position in relation to the substrate.
1. A plastic ball grid array semiconductor package comprising a metal heat spreader having supporting arms embedded in a molding cap, feet connected at peripheral ends of the supporting arms, wherein:
the feet have a level portion connected to the supporting arms and parallel with a substrate and an outer portion angled away from the substrate, and
the metal heat spreader is spaced away and physically isolated from the substrate by the molding cap between the supporting arms and the substrate and wherein the heat spreader is configured so that their lower ends do not contact the substrate surface.
2. The package of claim 1 wherein the heat spreader is constructed of metal.
3. The package of claim 2 wherein the heat spreader is constructed of copper.
4. The package of claim 1 wherein the heat spreader has four supporting arms, configured so that their lower ends do not contact the substrate surface in a generally rectangular array spaced away form the substrate.
5. The package of claim 4 wherein the heat spreader has four supporting arms, configured so that their lower ends do not contact the substrate surface in a generally square array spaced away from the substrate.
6. The package of claim 2 wherein an under surface of the metal heat spreader is chemically roughened at the interface of the heat spreader and the molding compound of the molding cap.
7. The package of claim 2 wherein an under surface of the metal heat spreader comprises a black copper oxide layer at the interface of the heat spreader and the molding compound of the molding cap.
8. The package of claim 6 wherein the roughened under surface of the heat spreader has a roughness in the range 0.5 um to 1.0 um.
9. The package of claim 8 wherein the roughened under surface of the heat spreader has a roughness of 0.5 um.
10. The package of claim 7 wherein the blackened copper oxide layer has a thickness in the range 3 um to 15 um.
11. The package of claim 10 wherein the blackened copper oxide layer has a thickness of 7 um.
12. The package of claim 2 wherein the heat spreader is constructed of copper.
13. The package of claim 1 wherein a portion of the heat spreader lying overlying the semiconductor device protrudes downward toward the upper surface of the semiconductor device, and a corresponding portion of the mold cap is thinner between the upper surface of the semiconductor device and the heat spreader than more peripherally.
14. A plastic ball grid array semiconductor package comprising a metal heat spreader having supporting arms embedded in a molding cap, feet connected at peripheral ends of the supporting arms, wherein:
the feet have a level portion connected to the supporting arms and parallel with a substrate and an outer portion angled away from the substrate, and
support arms are affixed to the substrate using a resilient material between the supporting arm and the substrate and contacting an outer surface of the outer portion and upper surface of the level portion, with the resilient material embedded in the molding cap.
15. The package of claim 14 wherein the resilient material has an elastic modulus in the range 0.5 MPa to 100 MPa.
16. The package of claim 15 wherein the resilient material has an elastic modulus in the range 1 MPa to 10 MPa.
17. The package of claim 15 wherein the resilient material has an elastic modulus of 5.5 MPa.
18. The package of claim 14 wherein the resilient material comprises an elastomeric adhesive.
19. The package of claim 18 wherein the elastomeric adhesive is a silicon adhesive.
20. The package of claim 14 wherein the heat spreader is constructed of metal.
21. The package of claim 14 wherein the heat spreader has four supporting arms, configured so that their lower ends contact the substrate surface in a generally rectangular array.
22. The package of claim 21 wherein the heat spreader has four supporting arms, configured so that their lower ends are spaced away from the substrate surface in a generally square array.
23. The package of claim 14 wherein a portion of the heat spreader lying overlying the semiconductor device protrudes downward toward the upper surface of the semiconductor device, and a corresponding portion of the mold cap is thinner between the upper surface of the semiconductor device and the heat spreader than more peripherally.
24. The package of claim 14 wherein the heat spreader is made of metal, and includes a black copper oxide layer on an undersurface of the metal heat spreader having the characteristic of treating the undersurface.
25. The package of claim 24 wherein the heat spreader includes the black copper oxide having the characteristics of treating the undersurface of the heat spreader with NaClO 2 .
26. The package of claim 24 wherein the heat spreader having the undersurface includes the undersurface having the characteristics of treating the undersurface with NaClO 2 under conditions sufficient to form a black copper oxide layer having a thickness in the range 3 um to 15 um.
27. The package of claim 26 wherein the heat spreader having the undersurface includes the undersurface having the characteristics of treating the undersurface with NaClO 2 under conditions sufficient to form a black copper oxide layer having a thickness of 7 um.