Circuitry for measuring mechanical stress impressed on a printed circuit board

• US 6,903,561 B2
• Filed: 04/08/2003
• Issued: 06/07/2005
• Est. Priority Date: 04/08/2003
• Status: Expired due to Fees

• Current Assignee: RPX Corporation
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Stephan, Frank M, Fairchild, M. Ray, Zhou, Jiming
• Primary Examiner(s): Deb, Anjan K.
• Application Number:
  US10/408,937
• Publication Number:
  US 20040201387A1
• Time in Patent Office: 791 Days
• Field of Search: 324/719, 324/71.1, 324/71.5, 339/47, 737/60, 737/63, 738/626.27, 737/74, 738/620.45, 361/784, 361/795, 338/47
• US Class Current: 324/719
• CPC Class Codes: G01L 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01M 5/0033 by determining damage, crack or wear
• CPC Class Codes: H05K 1/0268 for electrical inspection or testing
• CPC Class Codes: H05K 1/0271 Arrangements for reducing stress or warp in rigid printed circuit boards, e.g. caused by loads, vibrations or differences in thermal expansion
• CPC Class Codes: H05K 1/167 incorporating printed resistors
• CPC Class Codes: H05K 2203/162 Testing a finished product, e.g. heat cycle testing of solder joints patterns for electrical inspection or testing H05K1/0268
• CPC Class Codes: H05K 2203/163 Monitoring a manufacturing process

Abstract

A circuit for measuring mechanical stress impressed on a printed circuit board includes a number of electrically conductive pads formed on at least one outer surface of the printed circuit board, and a resistive material applied in a pattern to the printed circuit board and defining a resistor between first and second ones of the number of electrically conductive pads. The resistive material exhibits an electrical resistance that varies as the resistive material is deformed so that the resistor exhibits an electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the resistor. Any number of such resistors may be formed on or within the printed circuit board, and any such resistor may form part of an external resistor bridge network configured to monitor changes in its resistance value.

Claims

1. A circuit for measuring mechanical stress impressed on a printed circuit board, the circuit comprising:

a number of electrically conductive pads formed on an at least one outer surface of the printed circuit board; and

a resistive material applied in a pattern to the printed circuit board and defining a first resistor between first and second ones of the number of electrically conductive pads, the resistive material exhibiting an electrical resistance that varies as the resistive material is deformed so that the first resistor exhibits a first electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the first resistor, wherein the first resistor extends along a first edge of the printed circuit board.

2. The circuit of claim 1 wherein the resistive material further defines a second resistor between third and fourth ones of the number of electrically conductive pads, the second resistor extending along a second edge of the printed circuit board opposite the first edge, the second resistor exhibiting a second electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the second resistor.

3. The circuit of claim 2 wherein the resistive material further defines a third resistor between the second and third ones of the number of electrically conductive pads, the third resistor extending along a third edge of the printed circuit board, the third resistor exhibiting a third electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the third resistor.

4. The circuit of claim 3 wherein the resistive material further defines a fourth resistor between the third and fourth ones of the number of electrically conductive pads, the fourth resistor extending along a fourth edge of the printed circuit board, the fourth resistor exhibiting a fourth electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the fourth resistor.

5. The circuit of claim 1 wherein the resistive material further defines a second resistor between the second one and a third one of the number of electrically conductive pads, the second resistor extending along a second edge of the printed circuit board transverse to the first edge, the second resistor exhibiting a second electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the second resistor.

6. The circuit of claim 1 wherein the first and second ones of the number of electrically conductive pads are located adjacent to each other, and the first resistor extends about a periphery of the printed circuit board.

7. The circuit of claim 1 wherein the first resistor is configured to open circuit when the mechanical stress impressed on the printed circuit board exceeds a mechanical stress threshold.

8. A circuit for measuring mechanical stress impressed on a printed circuit board, the circuit comprising:

a number of electrically conductive pads formed on an at least one outer surface of the printed circuit board; and

a resistive material applied in a pattern to the printed circuit board and defining a first resistor between first and second ones of the number of electrically conductive pads, the resistive material exhibiting an electrical resistance that varies as the resistive material is deformed so that the first resistor exhibits a first electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the first resistor, wherein the first one of the number of electrically conductive pads is located substantially central to the printed circuit board and the second one of the number of electrically conductive pads is located adjacent to a first corner of the printed circuit board, the first resistor extending diagonally across the printed circuit board from the first one of the electrically conductive pads to the second one of the number of electrically conductive pads.

9. The circuit of claim 8 wherein the resistive material defines a second resistor extending diagonally across the printed circuit board between the first one of said number of electrically conductive pads and a third one of the number of electrically conductive pads located adjacent to a second corner of the printed circuit board, the second resistor exhibiting a second electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the second resistor.

10. The circuit of claim 9 wherein the resistive material defines a third resistor extending diagonally across the printed circuit board between the first one of the number of electrically conductive pads and a fourth one of the number of electrically conductive pads located adjacent to a third corner of the printed circuit board, the third resistor exhibiting a third electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the third resistor.

11. The circuit of claim 10 wherein the resistive material defines a fourth resistor extending diagonally across the printed circuit board between the first one of the number of electrically conductive pads and a fifth one of the number of electrically conductive pads located adjacent to a fourth corner of the printed circuit board, the fourth resistor exhibiting a fourth electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the fourth resistor.

12. A circuit for measuring mechanical stress impressed on a printed circuit board, the circuit comprising:

a number of electrically conductive pads formed on an at least one outer surface of the printed circuit board; and

a resistive material applied in a pattern to the printed circuit board and defining a first resistor between first and second ones of the number of electrically conductive pads, the resistive material exhibiting an electrical resistance that varies as the resistive material is deformed so that the first resistor exhibits a first electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the first resistor, wherein the printed circuit board includes a number of circuit board layers having electrically conductive circuit paths disposed between at least some of the number of circuit board layers;

and wherein the resistive material is applied in the pattern between one of the number of circuit board layers and an opposing one of the number of circuit board layers.

13. The circuit of claim 12 wherein the first resistor extends along first juxtaposed edges of the one of the number of circuit board layers and the opposing one of the number of circuit board layers.

14. The circuit of claim 13 wherein the resistive material further defines a second resistor between third and fourth ones of the number of electrically conductive pads, the second resistor extending along second juxtaposed edges of the one of the number of circuit board layers and the opposing one of the number of circuit board layers edges opposite the first juxtaposed edges, the second resistor exhibiting a second electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the second resistor.

15. The circuit of claim 14 wherein the resistive material further defines a third resistor between the second and third ones of the number of electrically conductive pads, the third resistor extending along third juxtaposed edges of the one of the number of circuit board layers and the opposing one of the number of circuit board layer, the third resistor exhibiting a third electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the third resistor.

16. The circuit of claim 15 wherein the resistive material further defines a fourth resistor between the third and fourth ones of the number of electrically conductive pads, the fourth resistor extending along fourth juxtaposed edges of the one of the number of circuit board layers and the opposing one of the number of circuit board layers edges, the fourth resistor exhibiting a fourth electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the fourth resistor.

17. The circuit of claim 12 wherein the first one of the number of electrically conductive pads is located substantially central to the printed circuit board and the second one of the number of electrically conductive pads is located adjacent to a first corner of the printed circuit board, the first resistor extending diagonally across the one of the number of circuit board layers and the opposing one of the number of circuit board layers between the first one of the electrically conductive pads and the second one of the number of electrically conductive pads.

18. The circuit of claim 17 wherein the resistive material defines a second resistor extending diagonally across the one of the number of circuit board layers and the opposing one of the number of circuit board layers between the first one of said number of electrically conductive pads and a third one of the number of electrically conductive pads located adjacent to a second corner of the printed circuit board, the second resistor exhibiting a second electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the second resistor.

19. The circuit of claim 18 wherein the resistive material defines a third resistor extending diagonally across the one of the number of circuit board layers and the opposing one of the number of circuit board layers between the first one of the number of electrically conductive pads and a fourth one of the number of electrically conductive pads located adjacent to a third corner of the printed circuit board, the third resistor exhibiting a third electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the third resistor.

20. The circuit of claim 19 wherein the resistive material defines a fourth resistor extending diagonally across the one of the number of circuit board layers and the opposing one of the number of circuit board layers between the first one of the number of electrically conductive pads and a fifth one of the number of electrically conductive pads located adjacent to a fourth corner of the printed circuit board, the fourth resistor exhibiting a fourth electrical resistance value that varies as a function of mechanical stress impressed on the printed circuit board sufficient to deform the resistive material defining the fourth resistor.