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Bed of Nails Fixture for Printed Circuit Board (PCB) Testing


Bed-of-Nails Test Fixture
Bed of Nails test Fixture used to test embedded control circuit boards.

The Challenge

We required a fixture to test and measure the quality and function of manufactured Printed Circuit Boards (PCBs).


The Solution

Using NI CompactRIO hardware and LabVIEW software we designed and built a bed of nails test fixture for the automated testing of circuit boards critical to the embedded control of other devices they’re deployed into.


Background

Circaflex is a reference architecture for the printed circuit board (PCB) design of embedded control systems. Embedded control systems are the circuit boards, aka “brains”, of any of the consumer electronic device. To ensure product function one must validate the quality of the circuit boards that control the product. This test and measurement process of circuit boards is automated using a bed of nails test fixture.

A bed of nails test fixture features a nest in which a circuit board rests. The board is met by a mechanical hood that features probes providing electrical connections between the fixture and the board. The location of the probes and the design of the nest requires custom fabrication specific to the circuit board being tested.


Programming is critical for a bed of nails fixture as hundreds of circuit board tests are sequenced and performed in a matter of minutes. These range from the high-precision measurement of voltage and current during board function, to the individual testing of board components. The LabVIEW software platform streamlines data acquisition during circuit board testing and accelerates the programming of test sequencing.


Left: A bed of nails test fixture is used to test Cyth’s Circaflex circuit boards. Right: The NI CompactRIO enables the fixture’s data acquisition.


Bed of Nails Fixture Process

  1. The operator places the circuit board in the provided nest.

  2. Control push buttons placed on the fixture’s side are pressed to enable the fixture’s mechanical hood to lower using a pneumatic slide.

  3. The electrical probes placed on the fixture’s hood make secure electrical contact and connection with the circuit board.

  4. The system begins the automated testing of the circuit board using scripted test sequencing.

  5. All tests data is acquired using high-speed data acquisition hardware and is recorded.

  6. A report is generated via an embedded PC which gives all test data including the pass and fail of individual tests.

  7. The mechanical hood is pneumatically released from the board and the operator repeats the process.


Delivering the Outcome

Our bed of nails test fixture allows for the accurate test and measurement of manufactured Printed Circuit Boards (PCBs). The fixture allows us to individually validate the function of each circuit board in minutes using the sequencing of predefined tests. The pairing of the mechanical fixture, NI CompactRIO data acquisition hardware, and programmed tests has significantly lowered our time and cost of test. The entire fixture was designed and built from a proof of concept into a finished product within 12 weeks.


Fixture Specifications

NI CompactRIO


Quantity

I/O Type

1

NI-9381, AI, 8 AO, 4 DIO, 0 V to 5 V, C Series Multifunction I/O Module

1

​NI-9264, 25 kS/s/ch Simultaneous, ±10 V, 16-Channel C Series Voltage Output Module

1

​NI-9219, 100 S/s/ch, 4-Channel C Series Universal Analog Input Module

1

NI-9264, 25 kS/s/ch Simultaneous, ±10 V, 16-Channel C Series Voltage Output Module



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