Thick film resistor, method of trimming thick film resistor, and printed circuit board having thick film resistor

• US 4,580,030 A
• Filed: 08/22/1984
• Issued: 04/01/1986
• Est. Priority Date: 08/26/1983
• Status: Expired due to Term

• Current Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Original Assignee: Victor Company of Japan Limited (JVC Kenwood Corporation)
• Inventors: Takeuchi, Makoto
• Primary Examiner(s): ALBRITTON, CLARENCE
• Application Number:
  US06/643,675
• Time in Patent Office: 587 Days
• Field of Search: 338/195, 338/308, 338/309, 338/314, 219/121 LH, 219/121 LJ, 29/610 R
• US Class Current: 219/121.69
• CPC Class Codes: H01C 1/034 the housing or enclosure being formed as coating or mould without outer sheath H01C1/032 takes precedence
• CPC Class Codes: H01C 17/006 adapted for manufacturing resistor chips
• CPC Class Codes: H01C 17/242 by laser trimming by laser in general B23K26/351
• CPC Class Codes: H01C 7/003 Thick film resistors
• CPC Class Codes: H05K 1/181 associated with surface mounted components

Abstract

A thick film resistor comprises a substrate made of a material which is uneasily damaged by a laser beam which impinges thereon, a resistor body formed on the substrate in the form of a thick film, and a pair of electrodes formed on the substrate. The electrodes are electrically connected to both ends of the resistor body, and the resistor body has a shape such that the substrate is exposed at least in a portion adjacent to one side edge of the resistor body.

Claims

1. A thick film resistor which is to be mounted on a first substrate, said thick film resistor comprising:

a second substrate made of a material which is not easily damaged by a laser beam impinging thereon;

a single resistor body formed on said second substrate in the form of a thick film;

a pair of electrodes formed on said second substrate, said electrodes being electrically connected to both ends of said single resistor body which is formed between said pair of electrodes;

a first coating for covering tops of said resistor body and said electrodes before said thick film resistor is subjected to a trimming process in which a part of said resistor body is removed by a laser beam, said first coating being a high temperature glass coating; and

a second coating for covering said resistor body and said first coating after said resistor body is subjected to said trimming process,

said single resistor body having such a shape that said second substrate is exposed in an exposed part which is adjacent to at least one side edge of said single resistor body, said exposed part having a dimension in accordance with a precision of mounting said thick film resistor on said first substrate so that the laser beam first impinges on said exposed part in the trimming process which is carried out in a state where said thick film resistor is directly mounted on said first substrate.

2. A thick film resistor as claimed in claim 1 in which said high-temperature glass comprises 45% to 60% by weight of minimum PbO, 20% to 35% by weight of quartz SiO₂, 5% to 15% by weight of boric acid B₂ O₃, and 2% to 10% by weight of aluminum oxide Al₂ O₃.

3. A thick film resistor as claimed in claim 1 in which said exposed part has a size such that a beam spot of the laser beam will not protrude from said exposed part.

4. A thick film resistor as claimed in claim 1 in which said thick film resistor is mounted on a printed circuit board comprising said first substrate and electrical circuitry mounted thereon, said thick film resistor being coupled to the circuitry on said printed circuit board and then being subjected to said trimming process.

5. A thick flim resistor as claimed in claim 4 in which said resistor body is subjected to said trimming process so that said resistor body has a predetermined resistance which causes the circuitry on said printed circuit board to have predetermined function and characteristic.

6. A thick film resistor as claimed in claim 4 in which said resistor body is subjected to said trimming process so that said resistor body has a predetermined resistance which causes a voltage across a reference point and a predetermined point in the circuitry on said printed circuit board to assume a predetermined voltage.

7. A thick film resistor as claimed in claim 4 in which said thick film resistor is electrically coupled to the electrical circuitry through conductors which are printed on one side of said first substrate, said thick film resistor being directly mounted on the other side of said first substrate.

8. A method of trimming a thick film resistor, said method comprising:

a first step of directly mounting said thick film resistor on a first substrate which is printed with conductors and is mounted with electrical circuit parts, said first substrate being made of a material susceptible to a leaser beam, said conductors electrically coupling said thick film resistor to said electrical circuit parts when said thick film resistor is mounted on said first substrate, said thick film resistor comprising a second substrate made of a material which is not easily damaged by a laser beam which impinges thereon, a single resistor body formed on said second substrate in the form of a thick film, said resistor body having such a shape that said second substrate is exposed at least in an exposed part which is adjacent to at least one side edge of said resistor body, a pair of electrodes formed on said second substrate so as to be connected to both ends of said resistor body, and a high-temperature glass coating for covering tops of said resistor body and said electrodes;

a second step of trimming and removing a part of said resistor body of said thick film resistor which is mounted on said first substrate, by applying a laser beam to said part of said resistor body, said exposed part having a dimension in accordance with a precision of mounting said thick film resistor on said first substrate in said first step so that said laser beam first impinges on said exposed part in said second step; and

a third step of coating a low-temperature resin coating on top of said thick film resistor which subjected to the trimming.

9. A method of trimming a thick film resistor as claimed in claim 8 in which said first step mounts said thick film resistor on one side of said first substrate, said one side of said first substrate being opposite to a side on which said conductors are printed.

10. A method as claimed in claim 8 in which said second step comprises a first substep of coupling a circuit for supplying a power source voltage and a signal and a measuring apparatus for measuring a characteristic of the circuit on said first substrate to said first substrate which is mounted with said thick film resistor, and a second substep of trimming and removing a part of said resistor body by the leaser beam while measuring the characteristic of the circuit on said first substrate by said measuring apparatus.

11. A method as claimed in claim 10 in which said second substep trims and removes the part of said resistor body while said measuring apparatus measures a voltage across a reference point and a predetermined point in the circuit on said first substrate, and stops the trimming of said resistor body when the measured voltage becomes equal to a predetermined voltage.

12. A printed circuit board characterized by being constituted by said first substrate and mounted with a thick film resistor which is trimmed according to the method of claim 8.