Multi-strand substrate for ball-grid array assemblies and method
View Patent ↗A multi-strand printed circuit board substrate for ball-grid array (BGA) assemblies includes a printed wiring board ( 11 ) having a plurality of BGA substrates ( 12 ) arranged in N rows ( 14 ) and M columns ( 16 ) to form an N by M array. N and M are greater than or equal to 2 and the size of the N by M array is selected such that each of the plurality of BGA substrates ( 12 ) maintains a planarity variation less than approximately 0.15 mm (approximately 6 mils). The printed wiring board ( 11 ) has a thickness ( 26 ) sufficient to minimize planarity variation and to allow a manufacturer to use automated assembly equipment without having to use support pallets or trays.
1. A method for assembling ball-grid array (BGA) packages, comprising the steps of:
providing a plurality of BGA substrates arranged in an N by M array within a printed circuit board having a thickness, wherein N and M are greater than or equal to 2, each BGA substrate having a plurality of bond posts and a plurality of contact pads;
attaching a semiconductor die to each of the plurality of BGA substrates, wherein each BGA substrate corresponds to an attached semiconductor die, each semiconductor die having a plurality of bond pads;
encapsulating the semiconductor die with an encapsulant;
curing the encapsulant; and
dividing the N by M array into separate BGA packages, wherein the size of the N by M array and the thickness of the printed circuit board are such that each of the plurality of BGA substrates maintains a planarity variation less than approximately 0.15 mm after assembly.
2. The method of claim 1 , wherein each of the plurality of BGA substrates corresponds to an individual device.
3. The method of claim 1 , wherein each of one of BGA substrates within the plurality of BGA substrates has a corresponding individual device within a plurality of individual devices.
4. The method of claim 1 , wherein the step of attaching comprises attaching a first die to a first one of the plurality of BGA substrates and attaching a second die to a second one of the plurality of BGA substrates.
5. The method of claim 1 , wherein the step of encapsulating the semiconductor die includes encapsulating with an encapsulant having a thermal coefficient of expansion close to that of the printed circuit board.
6. The method of claim 1 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a plurality of stress-relief slots at various locations within the printed circuit board.
7. The method of claim 1 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a thickness greater than approximately 0.5 mm.
8. The method of claim 1 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a width on an order of 63 mm.
9. The method of claim 1 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a length in a range from approximately 187 mm to 12 mm.
10. The method of claim 1 , wherein the at least one bond pad comprises copper or gold plated copper.
11. The method of claim 2 , wherein each of the individual devices comprises a semiconductor die.
12. The method of claim 6 , wherein at least one of the plurality of stress-relief slots is of a different size from another of the plurality of stress-relief slots.
13. The method of claim 10 , wherein the at least one bond pad is one of a solid metallization area or a patterned metallization area having a specific geometric shape, wherein the specific geometric shape is a cross or Union Jack.
14. The method of claim 2 , wherein the step of attaching comprises attaching a first die to a first one of the plurality of BGA substrates and attaching a second die to a second one of the plurality of BGA substrates.
15. The method of claim 14 , wherein the step of encapsulating the semiconductor die includes encapsulating with an encapsulant having a thermal coefficient of expansion close to that of the printed circuit board.
16. The method of claim 15 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a plurality of stress-relief slots at various locations within the printed circuit board.
17. The method of claim 16 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a thickness greater than approximately 0.5 mm.
18. The method of claim 17 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a width on an order of 63 mm.
19. The method of claim 18 , wherein the step of providing the plurality of BGA substrates arranged in the N by M array within the printed circuit board includes providing the plurality of BGA substrates within the printed circuit board having a length in a range from approximately 187 mm to 12 mm.
20. The method of claim 16 , wherein at least one of the plurality of stress-relief slots is of a different size from another of the plurality of stress-relief slots.
21. The method of claim 20 , wherein the at least one bond pad comprises copper or gold plated copper.
22. The method of claim 21 , wherein the at least one bond pad is one of a solid metallization area or a patterned metallization area having a specific geometric shape, wherein the specific geometric shape is a cross or Union Jack.