Method for depositing solder material on an electronic component part using separators
A method for accurately depositing a required volume of solder material on a specific area of a lead frame, substrate or other part of an electronic component to be bonded by reflow of solder material to another part into a reliable, void-free connection during a subsequent assembly step comprises the following steps. Minute particles of solder material whose cumulative volume corresponds to the total volume to be deposited are loaded into a cavity cut into a fixture made from a material such as graphite. The cavity delineates the specific area of deposit. The part is then laid upon the fixture and immobilized thereon by a cover made from a material such as graphite. The fixture and its enclosed part are then subjected to solder material melting temperature under a controlled atmosphere in a furnace. The cavity is patterned and dimensioned to accommodate the right number of uniformly dimensioned particles necessary to precisely create the desired deposit of solder material.
1. A method for accurately depositing a metered volume of solder material of a given melting point on a delineated area of an electronic component part, said method comprising the steps of:
providing a fixture having a top surface shaped and dimensioned for intimate contact with said area, and a melting temperature substantially higher than said melting point;
carving into said top surface a closed-ended cavity shaped to be congruent with said area, wherein said cavity has a series of spaced-apart bottom separators;
pouring into said cavity said solder material,
wherein said solder material is a plurality of substantially uniformly dimensioned flowable particles, and
wherein a single particle is intimately nested in and spaced apart by each separator;
positioning said part against said top surface and said particles in contact with said area; and
exposing said fixture and part to a temperature at least equal to said melting point;
wherein said particles melt and join together to cover and adhere to said area.
2. The method of claim 1 which further comprises securing said part upon said fixture with a cover.
3. The method of claim 1 , wherein said fixture is made of a material comprising high density graphite.
4. The method of claim 1 , wherein said solder material comprises a metal alloy selected from the group consisting of gold alloys, tin alloys, lead alloys, copper alloys, and silver alloys.
5. The method of claim 1 , wherein said solder material comprises a metal alloy selected from the group consisting of AuSn, AuGe, AuSi, AuAgCu, AgCu, and PbSnAg.
6. The method of claim 1 , wherein said delineated area comprises an electronic package lead frame.
7. The method of claim 1 , wherein said delineated area comprises a marginal, peripheral area of a microelectronic package lid.
8. The method of claim 1 , wherein said cavity is segmented into a plurality of ditches.
9. The method of claim 8 , wherein two of said plurality of ditches are differently dimensioned.
10. The method of claim 1 , wherein said particles are laid in a single row into said cavity.
11. The method of claim 1 , which further comprises vibrating said fixture to avoid clumping of said particles.
12. The method of claim 1 , wherein said particles are laid in a plurality of rows into said cavity.
13. The method of claim 1 , wherein said particles are symmetrical, and have calculated dimensions.
14. The method of claim 1 , wherein said particles are spherical, and have a calculated diameter and radius.
15. The method of claim 14 , wherein said cavity has a constant depth greater than said diameter.
16. The method of claim 14 , wherein said cavity has a constant depth lesser than said diameter.
17. The method of claim 14 , wherein said cavity has an arcuate bottom.
18. The method of claim 1 , which further comprises sweeping away an excess number of said particles.
19. The method of claim 1 , wherein said step of positioning comprises inverting said fixture and part.
20. The method of claim 1 , which further comprises pressing said part against said fixture.
21. The method of claim 1 , wherein said separators are regularly spaced-apart at a calculated interval.