Assembling a lead frame between a pair of molding cavity plates

• US 5,286,426 A
• Filed: 04/01/1992
• Issued: 02/15/1994
• Est. Priority Date: 04/01/1992
• Status: Expired due to Term

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Rano, Albert V. Jr., Tee, Benjamin O., Castro, Romeo R.
• Primary Examiner(s): Silbaugh, Jan H.
• Assistant Examiner(s): ORTIZ, ANGELA Y
• Application Number:
  US07/861,723
• Time in Patent Office: 685 Days
• Field of Search: 264/40.1, 264/40.5, 264/40.2, 264/272.15, 264/272.17, 425/171
• US Class Current: 264/40.1
• CPC Class Codes: B29C 45/14065 Positioning or centering articles in the mould
• CPC Class Codes: B29C 45/14655 connected to or mounted on a carrier, e.g. lead frame
• CPC Class Codes: B29C 45/842 Detection of insert defects, e.g. inaccurate position, breakage
• CPC Class Codes: H01L 21/565 Moulds
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/49171 Fan-out arrangements
• CPC Class Codes: H01L 24/97 the devices being connected to a common substrate, e.g. interposer, said common substrate being separable into individual assemblies after connecting
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/14 Integrated circuits
• CPC Class Codes: H01L 2924/181 Encapsulation

Abstract

In a method for assembling a lead frame between two plate-mold cavity plates, a lead frame that includes a plurality of integrated circuit chips mounted spaced at intervals in a row thereon, is placed on a bottom one of the cavity plates which has a row of cavities spaced apart at the same intervals as the integrated circuit chips, each chip being positioned over a corresponding cavity. The bottom cavity plate is held about horizontal on the base plate of an assembly fixture. Two short guide pins extend upward from the cavity plate, the lead frame having two pilot holes directly above the guide pins. Accurate positioning of the lead frame will permit penetration of the pilot holes by the guide pins. When inaccurate positioning occurs, the lead frame will ride up on the guide pin(s) admitting ambient light into light-detecting holes formed in the bottom cavity plate, and a light detection system in the assembly fixture, including photo-detectors at each hole and a signal generating circuit, will generate a warning signal that may in turn generate a warning light or sound to advise an operator to reposition the lead frame accurately.

Claims

1. A method for assembling a lead frame strip within a pair of mold plates to form a sandwich assembly ready for molding comprising:

a) placing a metal lead frame strip on a bottom one of a mating pair of mold plates, each of said mold plates having a row of cavities therein spaced apart by identical intervals, said lead frame strip having a multiplicity of electronic components mounted to said strip at intervals commensurate with the intervals of said cavities in said mold plates, said placing including positioning said electronic components over corresponding of said bottom-plate cavities, said bottom mold plate having two lead-frame guide pins extending upwardly therefrom, said lead frame strip having two pilot holes that at said positioning lie about registered with and directly above said two guide pins;

said bottom mold plate having two light-detection holes underlying metal portions of said lead frame that are not registered with any one of said bottom-plate cavities,

b) sensing whether light is being admitted in said light-detection holes;

c) generating a warning signal when light is sensed in one of said light-detection holes, indicating that one of said lead-frame pilot holes has into exactly registered with the corresponding of said guide pins, and that said lead frame strip rides upon on said corresponding guide pin and has not seated to said bottom mold plate so that ambient light is not blocked from entering said light-detection hole;

d) repositioning said unseated lead frame strip to a coarsely align said pins with said pilot holes and seat said lead frame strip flush with said bottom mold plate to block ambient light from said light detection holes; and

e) fitting the other one of said pair of mold plates over said bottom mold plate and lead frame strip.

2. A method for assembling a lead frame strip within a pair of mold plates comprising:

a) providing an assembly fixture having a horizontal base plate, two guide posts fixed to said base plate and extending upwardly therefrom;

b) fitting a bottom one of a pair of mold plates on and flush with said fixture base plate with said guide posts extending upwardly through corresponding guide holes provided therefor in said bottom mold late, said bottom molds plate having a row of cavities spaced at intervals in said row, said cavities extending through said bottom mold plate and having at least two lead-frame guide pins extending upwardly therefrom;

c) placing a metal lead frame strip on said bottom mold plate, said lead frame strip having a multiplicity of electronic components mounted to said strip at intervals commensurate with the intervals of said cavities in said bottom mold plate, said placing including positioning said electronic components over corresponding of said bottom-place cavities, said lead frame strip having two pilot holes that at said positioning lie about registered with and directly above said two guide pins;

said bottom mold place having two light-detection holes underlying said metal portions of said lead frame that are not registered with any one of said cavities,

d) sensing whether light is being admitted in said light-detection holes;

d) generating a warning signal when light is sensed in one of said light-detection holes, indicating that one of said lead-frame pilot holes has not exactly registered with the corresponding of said guide pins, and that said lead frame strip rides upon on said corresponding guide pin and has not seated to said bottom mold plate so that ambient light is not blocked from entering said light-detection hole; and

f) repositioning said unseated lead frame strip to accurately align said pins with said pilot holes and seat said lead frame strip flush with said bottom mold plate to block ambient light from said light detection holes.

3. The method of claim 2 additionally comprising fitting the top one of said pair of mold plates over said bottom mold plate and over said lead frame strip with said guide posts threaded into guide holes provided therefor in said top mold plate, said fitting including registering said top-place cavities over said bottom-plate cavities.