Method and apparatus for applying solder preforms
BACKGROUND AND SUMMARY OF THE INVENTION 
     Soldering connector pins to the plated-through holes of circuits boards is a labor intensive and tedious operation with many pitfalls. Too much solder may result in a short between two adjacent pins. Too little solder may result in an inadequate electrical connection between the pin and the plated-through hole. The right amount of solder wrongly placed results in too much solder on the surface of the circuit board and too little solder in the plated-through hole to make a connection that will withstand vibration. 
     Thus, the art has long sought a simple method that will ensure that the correct amount of solder is placed in the proper position around each pin and at each plated-through hole. 
     The invention overcomes the above-noted and other drawbacks of the prior art by providing a method for applying solder preforms to contacts of connectors which features a capability of depositing the exact amount of solder required in the exact position required. This invention eliminates that undesirable feature common to existing methods wherein the solder is sequentially applied to each individual contact of a connector. The invention is the first successful method of applying solder to connector contacts which simultaneously applies the desired amount of solder preforms in the correct position to all the contacts of a given connector. 
     In the method of the present invention, a water-soluble adhesive material is perforated to form perforations in a pattern according to the arrangement of the pins of a connector, solder preforms are applied around the perforations, the pins of the connector are inserted through the holes of a circuit board; and then the adhesive material is positioned against the circuit board to center the solder preforms around the pins. The adhesive material is then washed off, e.g., with water. Finally, the pins of the connector are heated to the flow-point temperature of the solder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates in a perspective view a connector, a printed circuit board, and a tape having solder preforms for soldering the pins of the connector to the printed circuit board; 
     FIG. 2 illustrates a tape perforated in accordance with the arrangement of the pins of the connector of FIG. 1; 
     FIG. 3 illustrates the tape of FIG. 1 and FIG. 2, with solder preforms attached, adjacent the printed circuit board of FIG. 1; 
     FIG. 4 is a side view illustrating the even distribution of the solder around the pins as the result of the method of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates in a perspective view a connector 10 having pins or contacts 12 spaced apart according to a given arrangement 14. Although a connector is shown, the method of the present invention is applicable to any pin device. Both FIG. 1 and FIG. 2 illustrate a strip 16 comprising an adhesive material perforated to form perforations 18 in a pattern corresponding to the arrangement 14. One suitable adhesive material takes the form of a tape. The tape preferably has adhesive material on one side only, but could have it on both sides. The tape is a water soluble, biodegradable tape such as Model No. YR-5414 sold by the 3M Company, St. Paul, MN. 
     Alternately, the adhesive material may take the form of a strip of non-adhesive material having regions of adhesive material around each perforation 18. 
     FIG. 2 illustrates the placing of solder preforms 20 on the adhesive material around each perforation 18. 
     Referring to FIG. 3, the connector 10 is attached to a circuit board 22 such that the pins 12 project through and extend beyond the circuit board 22. The side of the tape 16 with the preforms 20 is then placed adjacent the circuit board 22 with the perforations 18 aligned with the pins 12 so that the pins 12 project through the perforations and therefore through the solder preforms. The tape 16 is then removed by water wash-off or any other similar process. 
     Referring now to FIG. 4, known techniques are used to flow the solder preforms around the pins 12. Vapor reflow is one such technique. The solder preforms 20 melt and thus flow downwardly around the pins 12 forming an electrical connection between the pins 12 and the plated-through holes 24 of the circuit board 22. 
     Alternatively, the strip 16 may be comprised of material other than water soluble materials which allow it to be removed from the circuit board 22. For example, the strip 16 may be comprised of a flammable material where it is burned off during the solder flow process, or it may be a biodegradable material. 
     The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.