Method of making electronic entities
Many electronic entities such as integrated circuits and discrete power devices have contact pads formed from successively deposited layers of nickel and a second metal such as gold. The resulting pad structure is used to make external electrical connection such as solder connection. Problems associated with failure of such connections are avoidable by inspecting the surface of the nickel layer for excessive small particle formation.
1. A method of fabricating a plurality of electronic entities having an electroless nickel immersion/gold (ENIG) structure, said method comprising the steps of:
forming a first electrically conducting region overlying a substrate;
forming a second region comprising nickel overlying said first electrically conducting region;
determining the small particle density for a predetermined area of the surface of said second region for at least one of said electronic entities of said plurality, by analyzing said surface: and
continuing toward completion of at least some of said electronic entities of said plurality if said small particle density of said predetermined area, for said at least one of said electronic entities, is not greater than a maximum acceptable value for said small particle density, said continuing toward completion including forming a third region overlying said second region, said third region comprising a further metal that is higher on the electromotive force (EMF) scale than nickel.
2. The method of claim 1 , wherein said analyzing comprises inspecting by use of scanning electron microscopy.
3. The method of claim 1 , wherein said analyzing comprises inspecting by use of optical spectroscopy.
4. The method of claim 3 , wherein said optical spectroscopy comprises infrared spectroscopy.
5. The method of claim 1 , wherein said further metal comprises gold.
6. The method of claim 1 , wherein said further metal comprises palladium.
7. The method of claim 1 , wherein said continuing toward completion comprises making a solder connection at said ENIG structure.
8. The method of claim 1 , wherein said continuing toward completion is performed on all of said electronic entities of said plurality.
9. The method of claim 1 , wherein said determining the small particle density is performed on at least 10% of said electronic entities of said plurality.
10. The method of claim 9 , wherein said determining the small particle density is performed on each of said electronic entities of said plurality.
11. The method of claim 1 , wherein said determining the small particle density includes defining a small particle as a particle having a surface area of less than approximately 7 μm 2 .
12. The method of claim 1 , wherein said ENIG structure includes an electroless nickel/electroless palladium/immersion gold (ENEPIG) structure.
13. The method of claim 1 , wherein said maximum acceptable value for said small particle density is more than 10 small particles for any 10,000 μm 2 pad region.
14. The method of claim 13 , wherein a small particle is a particle having a surface area of less than approximately 7 μm 2 .