Method of forming a land grid array with discrete pads
A land grid array (LGA) and a method of forming the LGA are disclosed. The method comprises plating a printed circuit board to form a grid array of copper pads, and soldering a discrete pad over each of the plated copper pads in the grid array. The discrete pad is a solid object that can be handled and positioned independent of other discrete pads. Optionally, the method may further comprise measuring variations in flatness of the printed circuit board as a function of location in the grid array, and selecting individual discrete pads that each have a thickness selected for use at a particular location in the grid array so that the discrete pads provide a locus of exposed surfaces having greater flatness than the printed circuit board.
1. A method of forming a land grid array, comprising:
plating a printed circuit board to form a grid array of copper pads;
soldering a discrete pad over each of the plated copper pads in the grid array;
measuring variation in flatness of the printed circuit board as a function of location in the grid array; and
selecting individual discrete pads each have a thickness selected for use at a particular location in the grid array so that the discrete pads provide a locus of exposed surfaces having greater flatness than the printed circuit board.
2. The method of claim 1 , wherein the grid array of copper pads includes a via through each copper pad.
3. The method of claim 2 , further comprising:
covering the vias in a plurality of the plated metal pads with the discrete pads.
4. The method of claim 1 , further comprising:
individually positioning each of the selected discrete pads over the plated copper pad at the particular location.
5. The method of claim 1 , further comprising:
removably securing a plurality of the selected discrete pads onto a substrate,
positioning the substrate over the grid array with the plurality of selected discrete pads aligned over the plated metal pads of the grid array; and
removing the substrate and leaving the discrete pads in contact with the plated metal pads of the grid array.
6. The method of claim 1 , further comprising:
forming the discrete pads with a base metal core plated with one or more metals.
7. The method of claim 6 , further comprising:
varying the thickness of the base metal core among the individual discrete pads.
8. The method of claim 6 , wherein the base metal core is copper.
9. The method of claim 8 , further comprising:
plating the copper core of the discrete pads with another metal.
10. The method of claim 8 , further comprising:
plating the copper core on all sides with nickel.
11. The method of claim 10 , further comprising:
plating tin onto a proximal surface of the nickel-plated copper core; and
positioning the tin plated proximal surface for soldering to the plated copper pad.
12. The method of claim 10 , further comprising:
plating gold onto an exposed contact surface of the nickel-plated copper core, where the gold-plated contact surface forms a contact for a surface mounted component.