Test Probe Coated with Conductive Elastomer for Testing of Backdrilled Plated Through Holes in Printed Circuit Board Assembly

• US 20150015288A1
• Filed: 07/10/2013
• Published: 01/15/2015
• Est. Priority Date: 07/10/2013
• Status: Active Grant

• Current Assignee: Globalfoundries US Incorporated (GlobalFoundries, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Ma, Wai M.
• Granted Patent: US 9,459,285 B2
• Time in Patent Office: Days
• US Class Current: 324/754.03
• CPC Class Codes: G01R 1/06738 related to tip portion
• CPC Class Codes: G01R 1/06755 Material aspects
• CPC Class Codes: G01R 31/2808 Holding, conveying or contacting devices, e.g. test adapters, edge connectors, extender boards probe, multiprobe, probe manipulator or probe fixture G01R1/067

Abstract

A test probe is provided for probing signal information on a back-drilled plated through hole connector formed in a printed circuit board, where the test probe includes a conductive probe body with a distal tip region extending a predetermined minimum coverage length (L_TIP) that is longer than a recess depth dimension (D_PL) for a recessed plating layer formed in the back-drilled plated through hole connector with an elastomer test probe tip formed around the distal tip region and having a total tip width (W_TIP) which is compressed when inserted into the recessed plating layer formed in a back-drilled plated through hole connector, thereby establishing a conductive path between the conductive probe body and the recessed plating layer.

Claims

1. An electrical device for probing signal information on a back-drilled plated through hole connector formed in a printed circuit board, comprising:

a conductive probe body comprising a distal tip region extending a predetermined minimum coverage length (L_TIP) that is controlled to be longer than a recess depth dimension (D_PL) for a recessed plating layer formed in a back-drilled plated through hole connector to be probed; and

an elastomer test probe tip formed around the distal tip region of the conductive probe body and having a total tip width (W_TIP) that is controlled to be compressed when inserted into the recessed plating layer formed in a back-drilled plated through hole connector to be probed, thereby establishing a conductive path between the conductive probe body and the recessed plating layer.

2. The electrical device of claim 1, where the distal tip region of the conductive probe body has a surface finish that is disposed to promote adhesion of the elastomer test probe tip.

3. The electrical device of claim 1, where the total tip width (W_TIP) of the elastomer test probe tip is controlled to be smaller than a first width measure of a back-drilled plated through hole opening formed in the printed circuit board where the back-drilled plated through hole connector is located.

4. The electrical device of claim 1, where the elastomer test probe tip comprises a spray coated elastomer material comprising conductive particles dispersed throughout the elastomer material to provide a conductive path between the conductive probe body and the recessed plating layer when inserted and compressed into contact with the back-drilled plated through hole connector.

5. The electrical device of claim 1, where the elastomer test probe tip comprises a spray coated elastomer material comprising a mixture of melted rubber, metal particles, and a volatile solvent.

6. The electrical device of claim 1, where the elastomer test probe tip comprises a metal impregnated polymer formed to a uniform thickness around sides of the distal tip region such that the metal impregnated polymer is conductive when compressed by the recessed plating layer formed in a back-drilled plated through hole connector, and is not conductive when not compressed by the recessed plating layer formed in a back-drilled plated through hole connector.

7. The electrical device of claim 1, where the elastomer test probe tip comprises an electrically conductive polymer film impregnated with carbon or silver.

8. A method comprising:

forming a conductive elastomer tip structure on a conductive test probe, where the conductive elastomer tip structure has a predetermined geometry and total width dimension that is suitable for insertion into a back-drilled plated through hole to make electrical contact with a back-drilled plating layer in the back-drilled plated through hole.

9. The method of claim 8, further comprising inserting the conductive elastomer tip structure and part of the conductive test probe into a first back-drilled plated through hole of a printed circuit board to make electrical contact between the conductive test probe and a back-drilled plating layer in the first back-drilled plated through hole.

10. The method of claim 8, where forming the conductive elastomer tip structure comprises spray coating a metal impregnated elastomer material on a distal tip region of the conductive test probe to form a conformal layer having a total tip width that is controlled to be compressed when inserted into the back-drilled plating layer in the first back-drilled plated through hole to be probed, thereby establishing a conductive path between the conductive test probe and a back-drilled plating layer in the first back-drilled plated through hole.

11. The method of claim 8, further comprising forming a distal tip region of the conductive test probe to have a surface finish to promote adhesion between the conductive elastomer tip structure and the conductive test probe.

12. The method of claim 8, where forming the conductive elastomer tip structure comprises forming the conductive elastomer tip structure to extend over a distal tip region of the conductive test probe by a predetermined minimum coverage length (L_TIP) that is controlled to be longer than a recess depth dimension (D_PL) for a back-drilled plating layer in the back-drilled plated through hole.

13. The method of claim 8, where forming the conductive elastomer tip structure comprises spray coating an elastomer spray solution comprising a mixture of melted rubber, metal particles, and a volatile solvent.

14. The method of claim 13, where spray coating the elastomer spray solution comprises applying the elastomer spray solution to a distal tip region of the conductive test probe using a rotational spray pattern for a predetermined duration to form the conductive elastomer tip structure with a conformal layer having a uniform thickness around the distal tip region.

15. A method of probing a back-drilled plated through ho e in a printed circuit board, comprising:

providing a printed circuit board comprising a first back-drilled plated through hole to be probed, said first back-drilled plated through hole comprising a recessed plating layer recessed within a through hole via having a first via width dimension (W_VIA) by a recess depth dimension (D_PL);

positioning a test probe in alignment with the first back-drilled plated through hole, where the test probe comprises a conductive elastomer test probe tip structure formed on a distal tip region of the test probe to have a predetermined minimum coverage length and a predetermined maximum total thickness, where predetermined minimum coverage length is controlled to be longer than the recess depth dimension (D_PL), and where the predetermined maximum total thickness is controlled to be smaller than the first via width dimension (W_VIA); and

inserting the test probe into the first back-drilled plated through hole so that the conductive elastomer test probe tip structure makes contact with a surface of the recessed plating layer in the first back-drilled plated through hole, thereby establishing a conductive path between the test probe and the first back-drilled plated through hole.

16. The method of claim 15, where inserting the test probe comprises wiping a surface of the recessed plating layer in the first back-drilled plated through hole to remove a surface oxide on the recessed plating layer when the conductive elastomer test probe tip structure contacts the surface of the recessed plating layer.

17. The method of claim 15, where inserting the test probe comprises compressing the conductive elastomer test probe tip structure with the recessed plating layer formed in the first back-drilled plated through hole so that conductive particles in the conductive elastomer test probe tip structure are compressed together to form an electrical path between the recessed plating layer and the test probe.

18. The method of claim 15, where the conductive elastomer test probe tip structure comprises conductive particles dispersed within the conductive elastomer test probe tip structure that do not form an electrical path through the conductive elastomer test probe tip/structure unless the conductive elastomer test probe tip structure is compressed against the recessed plating layer formed in the first back-drilled plated through hole connector.

19. The method of claim 15, where the test probe inserted into the first back-drilled plated through hole comprises a metal impregnated polymer formed to a uniform thickness around sides of the distal tip region such that the metal impregnated polymer is conductive when compressed by the recessed plating layer formed in the first back-drilled plated through hole, and is not conductive when not compressed by the recessed plating layer formed in a first back-drilled plated through hole connector.

20. The method of claim 15, where the test probe inserted into the first back-drilled plated through hole comprises a spray coated elastomer material comprising conductive particles dispersed throughout the elastomer material to provide a conductive path between the test probe and the recessed plating layer when inserted and compressed into contact with the recessed planting layer in the first back-drilled plated through hole.