System and method for detecting shorts, opens and connected pins on a printed circuit board using automatic test equipment

• US 6,291,978 B1
• Filed: 07/26/1999
• Issued: 09/18/2001
• Est. Priority Date: 08/31/1993
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Boswell, Bryan D., Heumann, John M., Chandler, Kevin G., Schlotzhauer, Ed O., Alcorn, Barry A.
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): LEROUX, ETIENNE PIERRE
• Application Number:
  US09/361,369
• Time in Patent Office: 785 Days
• Field of Search: 324/73.1, 324/754, 324/158.1, 324/765, 324/537, 324/158 R, 324/501, 324/763
• US Class Current: 324/73.1
• CPC Class Codes: G01R 31/2812 Checking for open circuits or shorts, e.g. solder bridges; Testing conductivity, resistivity or impedance of connections G01R31/66
• CPC Class Codes: G01R 31/318342 by preliminary fault modelling, e.g. analysis, simulation
• CPC Class Codes: G01R 31/3191 Calibration
• CPC Class Codes: G01R 31/31915 In-circuit Testers

Abstract

A method for testing node interconnection on a circuit board. The method utilizes an automated test system having at least one test channel, wherein each test channel has a digital driver with a first input and a first output, and a digital receiver with a second output and a second input. The second input of the receiver is coupled to the first output of the driver and to a test probe. The test probe is configured to couple the driver and receiver to one of a plurality of nodes on a circuit board. During a node interconnection test, the driver of a first test channel applies a test signal to a selected node of the plurality of nodes. A predetermined amount of time after application of the test signal, the receiver of the first test channel reads a node voltage of the selected node. The node voltage is then compared to a predetermined threshold voltage of the receiver of the first test channel, and the result of the comparison is an indication as to whether the selected node is coupled to ground.

Claims

1. A method for testing node interconnection on a circuit board having a plurality of nodes using an automated test system comprising at least one test channel, each of the at least one test channel comprising a digital driver having a first input and a first output, a digital receiver having a second output and a second input, the second input being coupled to the first output, and a test probe, the test probe being coupled to the first output and the second input, and the test probe being configured to couple the first output and second input to one of the plurality of nodes, the method comprising:

(a) said digital driver of a first test channel applying a test signal to a selected node of the plurality of nodes;

(b) a predetermined amount of time after said application of said test signal, said digital receiver of the first test channel reading a node voltage of said selected node;

(c) comparing said node voltage to a predetermined threshold voltage of said digital receiver of the first test channel; and

(d) indicating whether said selected node is coupled to ground based on said comparison of said node voltage to said threshold voltage.

2. A method as in claim 1, wherein said test signal applied by said digital driver of the first test channel is a low powered digital signal which is incapable of activating semiconductor junctions located on the circuit board.

3. A method as in claim 1, further comprising calibrating said digital driver of the first test channel so that said test signal has a voltage sufficiently low such that applying said test signal to the circuit board does not activate semiconductor junctions located on the circuit board.

4. A method as in claim 1, wherein:

(a) the first output of the first test channel comprises an incline impedance having a known value; and

(b) said known value contributes in determining said predetermined threshold voltage.

5. A method as in claim 1, wherein said predetermined amount of time is a function of an impedance-capacitance time constant of said selected node.

6. A method as in claim 1, further comprising, prior to application of said test signal, coupling a second node of the plurality of nodes on said circuit board to ground.

7. A method as in claim 6, wherein said coupling of said second node to ground comprises:

(a) placing said test probe of a second test channel in contact with said second node; and

(b) closing a number of switches of said second test channel to couple said second node to ground.

8. A method as in claim 1, further comprising, if said selected node is not coupled to ground:

(a) coupling a second node of the plurality of nodes on said circuit board to ground;

(b) applying a test signal to said selected node via said digital driver of the first test channel;

(c) a predetermined amount of time after said application of said test signal, reading a node voltage of said selected node via said digital receiver of the first test channel;

(d) comparing said node voltage of said selected node to said predetermined threshold voltage of said digital receiver of the first test channel; and

(e) indicating whether said selected node is coupled to said second node based on said comparison of said node voltage of said selected node to said threshold voltage of said digital receiver of the first test channel.

9. A system as in claim 8, wherein said coupling of said second node to ground comprises:

(a) placing said test probe of a second test channel in contact with said second node; and

(b) closing a number of switches of said second test channel to couple said second node to ground.

10. A method as in claim 1, wherein said selected node is a member of a group of nodes on said circuit board, the method further comprising, prior to application of said test signal, coupling all nodes in said group of nodes, but for said selected node, to ground so that said indication is an indication of whether said selected node is isolated from the remaining nodes of said group of nodes.

11. A method as in claim 10, wherein said coupling of a given node in said group of nodes to ground, comprises:

(a) placing said test probe of a given test channel in contact with said given node; and

(b) closing a number of switches of said given test channel to couple said second node to ground.

12. A method as in claim 10, further comprising, if said selected node is not isolated from said remaining nodes of said group of nodes:

(a) releasing all nodes in said group of nodes from ground couplings which are not predetermined by the structure of said circuit board; and

(b) determining if said selected node is directly coupled to ground.

13. A method as in claim 12, wherein determining if said selected node is directly coupled to ground comprises:

(a) said digital driver of the first test channel applying a test signal to said selected node;

(b) a predetermined amount of time after said application of said test signal, said digital receiver of the first test channel reading a node voltage of said selected node;

(c) comparing said node voltage to said predetermined threshold voltage of said digital receiver of the first test channel; and

(d) indicating whether said selected node is coupled to ground based on said comparison of said node voltage to said threshold voltage.

14. A method as in claim 12, further comprising, if said selected node is not isolated from said remaining nodes of said group of nodes, and said selected node is not directly coupled to ground, and it is not yet known which of said nodes in said group of nodes said selected node is connected to, coupling varying subsets of nodes in said group of nodes to ground, and for each subset of nodes so coupled:

(a) applying a test signal to said selected node via said digital driver of the first test channel;

(b) a predetermined amount of time after said application of said test signal, reading a node voltage of said selected node via said digital receiver of the first test channel;

(c) comparing said node voltage to said predetermined threshold voltage of said digital receiver of the first test channel; and

(d) indicating whether said selected node is isolated from said subset of nodes based on said comparison of said node voltage to said threshold voltage.

15. A method as in claim 14, wherein each of said varying subsets of nodes in said group of nodes comprises half of the nodes in a subset of nodes for which isolation from said selected node has already been determined.

16. A method as in claim 1, wherein said automated test system comprises a plurality of test channels.

17. A method as in claim 16, wherein each of said plurality of test channels comprises a number of switches coupled to a test channel'"'"'s first output and second input, said number of switches being configured to selectively couple the first output and the second input of their test channel to ground.

18. A method as in claim 17, wherein said selected node is a member of a group of nodes on said circuit board, the method further comprising, if said selected node is not coupled to ground:

(a) for each of said nodes in said group of nodes, placing a test probe of a different one of the plurality of test channels in contact with said node;

(b) closing said number of switches of a second test channel to couple a second node of said group of nodes to ground;

(c) applying a test signal to said selected node via said digital driver of the first test channel;

(d) a predetermined amount of time after said application of said test signal, reading a node voltage of said selected node via said digital receiver of the first test channel;

(e) comparing said node voltage to said predetermined threshold voltage of said digital receiver of the first test channel;

indicating whether said selected node and said second node are coupled to one another based on said comparison of said node voltage to said threshold voltage; and

(g) opening said number of switches of said second test channel and repeating steps (b)-(f) for said selected node, in combination with each other node in said group of nodes.

19. A method as in claim 17, wherein said selected node is a member of a group of nodes on said circuit board, the method further comprising, prior to application of said test signal:

(a) for each of said nodes in said group of nodes, placing a test probe of a different one of the plurality of test channels in contact with said node;

(b) closing said number of switches of each test channel connected to a node in said group of nodes, but for said number of switches of the first test channel, so as to couple each node in said group of nodes, but for said selected node, to ground so that said indication is an indication of whether said selected node is isolated from the remaining nodes of said group of nodes;

(c) if said selected node is not isolated from said remaining nodes of said group of nodes,

(i) opening said n umber of switches of each test channel connected to a node in said group of nodes; and

(ii) determining if said selected node is directly coupled to ground;

(d) if said selected node is not isolated from said remaining nodes of said group of nodes, and said selected node is not directly coupled to ground, and it is not yet known which of said nodes in said group of nodes said selected node is connected to, coupling varying subsets of nodes in said group of nodes to ground, and for each subset of nodes so coupled;

(i) applying a test signal to said selected node via said digital driver of the first test channel;

(ii) a predetermined amount of time after said application of said test signal, reading a node voltage of said selected node via said digital receiver of the first test channel;

(iii) comparing said node voltage to said predetermined threshold voltage of said digital receiver of the first test channel; and

(iv) indicating whether said selected node is isolated from said subset of nodes based on said comparison of said node voltage to said threshold voltage.

20. A method as in claim 19, wherein each of said varying subsets of nodes in said group of nodes comprises half of the nodes in a subset of nodes for which isolation from said selected node has already been determined.