Multi-strand substrate for ball-grid array assemblies and method

Abstract

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 .- 20 . (canceled) 
     
     
         21 . 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 of the plurality of BGA substrates having a plurality of bond posts on one side and a plurality of contact pads on an opposite side, wherein the thickness of the printed circuit board is selected such that the printed circuit board can be subjected to automated assembly processes without using a metal support pallet;   attaching a semiconductor die to each of the plurality of BGA substrates, the semiconductor die having at least one bond pad;   encapsulating the semiconductor die with an encapsulant;   curing the encapsulant;   attaching conductive solder balls to each of the plurality of contact pads; and   dividing the N by M array into separate BGA packages.   
     
     
         22 . The method of  claim 21 , wherein the step of encapsulating the semiconductor die includes encapsulating with an encapsulant having a thermal coefficient of expansion close to that of the semiconductor die and the printed circuit board. 
     
     
         23 . The method of  claim 21 , 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. 
     
     
         24 . The method of  claim 21 , 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. 
     
     
         25 . The method of  claim 21 , 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. 
     
     
         26 . The method of  claim 21 , 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 212 mm. 
     
     
         27 . The method of  claim 21  further comprising the steps of:
 bonding conductive wires to the plurality of bond pads and the plurality of bond posts after the step of attaching the semiconductor die; and   marking the BGA packages after the step of over-molding the semiconductor die.   
     
     
         28 . The method of  claim 21 , wherein the step of curing the encapsulant further includes protecting the plurality of contact pads from foreign matter contamination. 
     
     
         29 . The method of  claim 21  further comprising, after attaching conductive solder balls to each of the plurality of contact pads, removing at least some corrosive residue from the printed circuit board. 
     
     
         30 . The method of  claim 23 , 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. 
     
     
         31 . The method of  claim 21 , wherein the printed circuit board further comprises a plurality of alignment holes on only one side of the printed circuit board. 
     
     
         32 . The method of  claim 21 , wherein the printed circuit board further comprises a plurality of alignment holes on both sides of the printed circuit board. 
     
     
         33 . The method of  claim 21 , wherein the at least one bond pad comprises copper or gold plated copper. 
     
     
         34 . The method of  claim 21 , wherein the at least one bond pad is a solid metallization area. 
     
     
         35 . The method of  claim 21 , wherein the at least one bond pad is a patterned metallization area having a specific geometric shape, wherein the specific geometric shape is a cross or Union Jack. 
     
     
         36 . The method of  claim 21 , wherein attaching conductive solder balls to each of the plurality of contact pads comprises attaching the conductive solder balls at room temperature. 
     
     
         37 . The method of  claim 36  further comprising, after attaching the conductive solder balls, reflowing the conductive solder balls using an automated solder reflow process. 
     
     
         38 . A ball-grid array (BGA) package, comprising:
 a BGA substrate formed from BGA substrates arranged in a N by M array within a printed circuit board having a thickness, wherein N and M are greater than or equal to 2, the BGA substrate having a plurality of bond posts and a plurality of contact pads, wherein a size of the N by M array is selected such that the BGA substrate maintains a planarity variation less than approximately 0.15 mm after assembly;   at least one semiconductor die coupled to the BGA substrate using the plurality of bond posts; and   an encapsulant formed over the at least one semiconductor die.   
     
     
         39 . The BGA package of  claim 38  further comprising solder balls attached to each of the plurality of contact pads. 
     
     
         40 . A ball-grid array (BGA) package, comprising:
 a BGA substrate divided from BGA substrates arranged in a N by M array within a printed circuit board having a thickness, wherein N and M are greater than or equal to 2, the BGA substrate having a plurality of bond posts and a plurality of contact pads, wherein the thickness of the printed circuit board is selected such that the BGA substrate maintains a planarity variation less than approximately 0.15 mm after assembly;   at least one semiconductor die coupled to the BGA substrate using the plurality of bond posts; and   an encapsulant formed over the at least one semiconductor die.   
     
     
         41 . The BGA package of  claim 40  further comprising solder balls attached to each of the plurality of contact pads. 
     
     
         42 . A ball-grid array (BGA) package, comprising:
 a BGA substrate divided from BGA substrates arranged in a N by M array within a printed circuit board having a thickness, wherein N and M are greater than or equal to 2, the BGA substrate having a plurality of bond posts and a plurality of contact pads, wherein a size of the N by M array and the thickness of the printed circuit board is selected such that the BGA substrate maintains a planarity variation less than approximately 0.15 mm after assembly;   at least one semiconductor die coupled to the BGA substrate using the plurality of bond posts; and   an encapsulant formed over the at least one semiconductor die.   
     
     
         43 . The BGA package of  claim 42  further comprising solder balls attached to each of the plurality of contact pads.