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Pressurized injection nozzle for screening paste
| Details |
Inventors: Gaynes, Michael A.; Oxx, George D.; Pierson, Mark V.; Zalesinski, Jerzy;
Assignee: International Business Machines Corporation (Armonk, NY)
Primary Examiner: Czaja; Donald E.
Assistant Examiner: Leavitt; Steven B.
Attorney, Agent or Firm: Whitham, Curtis, Whitham & McGinn, Belk; Michael E.
A method of applying bonding agents, such as solder pastes and conductive adhesives, to pad sites in the manufacture of electronic circuits uses a paste injection head. A permanent mask with cavity openings is applied around conductive pads on a carrier. The conductive pads correspond to chip attachment sites. The injection head is brought into contact with a surface of the mask, and pressure is applied to a bonding agent in the injection head. The injection head is then moved over the surface of the mask, filling cavity openings with the bonding agent. The injection head is then removed from the surface of the mask. If a solder paste is used, infrared radiation is applied to filled cavity openings to evaporate a paste flux and reflow solder to form solder balls within the cavity openings projecting above the mask. If a conductive adhesive is used, a stencil is applied to the surface of the mask prior to contacting the mask with said injection head. When the cavity openings are filled, stencil is removed from the mask and the conductive adhesive filling the cavity openings is dried. |
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DETAILED DESCRIPTION It is therefore an object of the present invention to provide an improved method of applying bonding agents, such as solder pastes and conductive adhesives, to chip on a chip carrier in the manufacture of electronic circuits.
It is another object of the invention to provide a method of applying a defined volume of solder paste to all pads on a chip site.
It is a further object of the invention to provide a method of fine pitch, screen printing of electrically conductive adhesives in one pass to interconnection sites.
According to one aspect of the invention, there is provided a solder paste injection process that quickly and inexpensively adds a defined volume of solder to each pad on a site.
The solder paste inject process pushes pressurized paste through a slit into cavities or blind holes formed by a mask (a procoat or solder shield) at each pad on the site.
The paste inject head lowers until the bottom surface contacts the mask.
A slight downward force is applied to keep the valving surfaces in intimate contact with the mask surface.
Pressure is applied to the paste.
The paste inject head moves across the site, filling the cavities.
As the paste inject head completes a site, the nozzle stops on the other side of the site.
The paste pressure is released to avoid leaving a small volume of paste on the procoat.
When the pressure is released, the nozzles are designed to relax and close, because the thin walls of the head are made to flex under pressure.
The inject head retracts upward.
According to another aspect of the invention, there is provided a process which makes possible screening the desired volume of conductive paste in one pass followed by a solvent evaporation step.
A permanent mask with cavities or blind holes around the conductive pads is applied to the panel or chip surface using well known techniques such as photolithography or screen printing.
The thickness of the mask is similar to the desired thickness of the electrically conductive adhesive.
Using existing screening technology, a thin (0
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Nonmetallic Processes 
