Detection of catastrophic failure of dielectric, improper connection, and temperature of a printed circuit assembly via one wire

• US 4,504,782 A
• Filed: 07/06/1982
• Issued: 03/12/1985
• Est. Priority Date: 07/06/1982
• Status: Expired due to Term

• Current Assignee: Sperry Corporation (Unisys Corporation)
• Original Assignee: Sperry Corporation (Unisys Corporation)
• Inventors: Zbinden, Terry B.
• Primary Examiner(s): Tokar, Michael J.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US06/395,511
• Time in Patent Office: 980 Days
• Field of Search: 324/73 PC, 324/54, 324/51, 324/52
• US Class Current: 324/551
• CPC Class Codes: G01R 31/2805 Bare printed circuit boards
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: H05K 1/0268 for electrical inspection or testing
• CPC Class Codes: H05K 1/0298 Multilayer circuits

Abstract

A first sensor for the detection of dielectric failure (by burning) within a multilayer printed circuit assembly comprises an isolated conductive layer. This first sensor is connected by a first diode to a single wire which also connects a second, temperature, sensor via a second diode (system ground is a return). A multiplicity, nominally 16, of such single wire connected sensor pairs are selectable in accordance with an externally (microprocessor) furnished address. During a first time period, an externally (microprocessor) selected interrogation of temperature causes a first, positive, voltage bias to be applied to the selected sensor pair resulting in a current linear with temperature (over the range of 0° C. to 100° C.) in the second sensor. This current is transformed to voltage, offset by 273° Kelvin, amplified, and converted to a digital value for issuance to an external (microprocessor) requestor. During a second time period, an externally (microprocessor) selected interrogation of dielectric failure causes a second, negative, voltage bias to be applied to the selected sensor pair. Any current sensed--which represents failure shorts between the isolated conductive layer and any other voltage, ground, or signal within the multilayer printed circuit assembly--is transformed to voltage, amplified, digitalized and issued externally. If neither temperature nor dielectric leakage currents can be properly sensed, and especially for plural addressable sensor pairs upon the same printed circuit assembly, then the assembly is deemed to be unconnected or improperly pluggably connected. Temperature (over temperature), dielectric failure, and failed connection are cyclically continuously monitored for a multiplicity of sensor pairs upon a plurality of printed circuit assemblies with an individual sensor test, or interrogation, time of 50 milliseconds.

Claims

1. A method of detecting the breakdown by burning of the electrically insulating dielectric within a multilayer printed circuit board, said method comprising:

establishing an electrically conductive layer within said multilayer printed circuit board which is normally continually electrically isolated by electrically insulating dielectric from any other voltage, signal, or ground as is transmitted upon other layers of said multilayer printed circuit board during operational usage of said multilayer printed circuit board;

electrically biasing during operational usage of said multilayer printed circuit board said electrically isolated conductive layer with a first voltage of greater voltage magnitude than any other voltage, signal, or ground as is transmitted upon other layers of said multilayer printed circit board during said operational usage of said multilayer printed circuit board;

sensing during operational usage of said multilayer printed circuit board said first voltage in order to determined IF a first level of said first voltage is sensed THEN substantially no current leakage between said electrically isolated layer and any other said voltage, signal, or ground within said multilayer printed circuit board is transpiring ELSE IF a second level of said first voltage is sensed THEN conductive current flow is transpiring between said electrically isolated layer and at least some one of said other voltage, signal, or ground within said multilayer printed circuit board;

wherein said sensing determination of said second level of said first voltage means that said dielectric electrically insulating said isolated conductive layer from at least some one of said other voltage, signal, or ground within said multilayer pritned circuit board has failed by becoming electrically conductive which occurs through carbonization attendant upon burning during said operational usage of said multilayer printed circuit board.

2. The dielectric breakdown defection method of claim 1 wherein said electrically biasing further comprises:

electrically biasing through a diode said electrically isolated conductive layer with a first voltage which is both of correct polarity to forward bias said diode and which is of greater voltage magnitude than any other voltage, signal, or ground as is transmitted upon other layers of said multilayer printed circuit board.

3. The dielectric breakdown detection method of claim 2 wherein said electrically biasing further comprises:

electrically biasing upon a first time period through a diode said electrically isolated conductive layer with a first voltage which is both of correct polarity to forward bias said diode and which is of greater voltage magnitude than any other voltage, signal, or ground as is transmitted upon other layers of said multilayer printed circuit board, and electrically biasing upon a second time period said diode with a second voltage which reverse biases said diode;

thereby electrically isolating through said diode said conductive layer during said second time period.

4. A circuit apparatus for detecting the breakdown into conduction of the normally electrically insulating dielectric of a multilayer printed circuit board, said apparatus comprising:

a electrically conductive layer within said multilayer printed circuit board normally continually electrically isolated by electrically insulating dielectric from any other voltage signal, or ground as is transmitted upon other layers of said multilayer printed circuit board during operational usage of said multilayer printed circuit board;

voltage biasing means connected to said conductive layer for charging during operational usage of said multilayer printed circuit board said normally electrically isolated conductive layer to a non-zero voltage; and

sensing means connected to said conductive layer for determining during operational usage of said multilayer printed circuit board if said non-zero voltage biased said normally electrically isolated conductive layer does connect to any one or ones of other voltages, signals, and ground as occur on other conductive layers of said multilayer pritned circuit card;

wherein if said normally isolated conductive layer is sensed during operational usage of said multilayer printed circuit board to be connecting to other voltages, signals, and/or grounds then said insulating dielectric of said printed circuit card has broken down into conduction.

5. The dielectric breakdown sensing apparatus of claim 4 which further comprises:

digitalizing means for converting said determining of said sensing means into digital data for transmission upon a digital interface.

6. A method for sensing upon a first time the failure of the dielectric and upon a second time the temperature of a multilayer printed circuit card, said method comprising:

electrically connecting a first end of a first diode to a conductive burn sensor layer, said burn sensor layer normally continually electrically isolated from all other conductive layers, including the layer carrying signal ground, within said multilayer printed circuit card during operational usage of said multilayer printed circuit board;

electrically connecting a second end of a second diode to a temperature sensor/transducer generating current responsively to temperature located upon said printed circuit card, which sensor/transducer is also electrically connected to signal ground;

electrically wire connecting said second end of said first diode and said first end of said second diode and a voltage biasing and sensing circuit, with said signal ground as a signal return path;

then upon a first time

first voltage biasing with said voltage biasing and sensing circuit upon said first time said second end of said first diode in a polarity wherein said first diode conducts current, while said first voltage biasing of said first end of said second diode causes said second diode not to conduct current;

while

first electrically sensing with said voltage biasing and sensing circuit upon said first time if current responsive to said first voltage biasing is conducted through said current conducting first diode and through said conductive burn sensor layer to any others of said conductive layers within said multilayer printed circuit card from which said conductive burn sensor layer is normally electrically isolated;

then upon a second time

second voltage biasing with said voltage biasing and sensing circuit upon said second time said first end of said second diode in a polarity wherein said second diode conducts current, while said second voltage biasing of said second end of said first diode causes said first diode not to conduct current;

while

second electrically sensing with said voltage biasing and sensing circuit upon said second time such conduction of current responsive to said second voltage biasing as occurs through said current conducting second diode and said temperature sensor/transducer;

wherein said first time first electrically sensing of any current conduction is an indication of the failure of the dielectric insulation upon said multilayer printed circuit card;

wherein said second time second electrically sensing of current conduction is an indication of the temperature of said temperature sensor/transducer upon said printed circuit card.

7. The dielectric failure and temperature sensing method of claim 6 which further comprises:

first performing said first voltage biasing and said first electrically sensing responsively to a first directive received upon a digital interface to said voltage biasing and sensing circuit, and second performing said second voltage biasing and said second electrically sensing responsively to a second directive received upon said digital interface; and

first digitalizing in an analog to digital converter results of said first electrically sensing for transmission upon said digital interface responsively to said first directive, and second digitalizing in said analog to digital converter results of said second electrically sensing for transmission upon said digital interface responsively to said second directive.

8. The dielectric failure and temperature sensing method of claim 6 which further comprises:

first performing and first digitalizing, and second performing and second digitalizing, as directed upon said digital interface for a selected and addressed one of a multiplicity of said diode connected burn sensor layers connected to a multiplicity of said temperature sensors/transducers as are located upon a plurality of said multilayer printed circuit cards, said selected and addressed one of said multiplicity being selected and addressed in a multiplexor responsively to said direction upon said digital interface.