The bed of nails
test fixture is a very commonly used testing fixture that performs in-circuit
testing. It has many pinouts configured in holes existing on epoxy-phenolic
glass cloth laminated sheets. This sheet was properly aligned by using pins of
tools for making connections with testing pins on board and wire used for
connection with measuring units. It is so-called since it is like the bed of
nails with small, spring-loaded pogo pins. Here we come to different features
and importance of the Bed of Nails test fixture. So let's get started.
What
is Bed of Test Fixtures?
Bed of Nails Test
is a standard testing process that is employed for testing components online to
find the manufacturing faults of the board and faulty components on boards
through the use of electrical features of fixtures. Another name for this
testing fixture is the ICT test fixture. The basic purpose of using this
process is to find open circuits or short circuits or inspect the welding on
board. It is mainly part of the bulk volume production of boards. The first
step of this test involves online testing of the board, detecting errors or
faults early and suggesting necessary changes.
In bed of nails
testing, the faults are found on components connected on board and pinout, and
it helps to increase efficiency and production process and reduce repair costs.
It is automated testing that helps not to get services from any professionals since
it is a simple and fast testing technique that can find and detect all faults
on board.
Bed
of Nails Test Fixture Design
Pogo Pins Arrangement
Pogo pins are
configured in a grid array of rows and are compatible with board connections
where testing is performed. All layouts of pins are set based on the design of
the board or device under testing. The pins are at a lower distance from
others, which helps to avoid short circuits between pins.
Material Selection
The base of the
bed of nails test fixture is typically made from aluminum or high-density
materials. Pins are made with stainless steel plated with gold, which reduces
the corrosion of pins and increases conductivity. Pogo pins are insulated to
avoid short circuits.
Customization
Options
The fixture must
be designed according to device designs that are under testing or board. There
is a need to provide some options that can increase or decrease the number of
pogo pins according to the device's structure. Pins are accurately labeled with
relevant workings, so no wrong pins are used for any test.
Integration with
Test Equipment
During the testing
process, a strong connection between testing devices and pogo pins is made;
wires or connectors are used for that purpose. It is also helpful for the easy
flow of signals and avoiding interference and noise.
Benefits
of the Test Fixture
High
Speed
This testing
fixture increases the testing process speed, so it is the best option for using
a larger volume manufacturing process since it helps to find faults fast and
removes errors on board.
Reliability
This test is
reliable and provides quality products since a direction connection is made
with testing points, and error-free results of tests are obtained.
Low-Cost
Test
While the initial
setup cost may be high, the fixture can test multiple boards simultaneously,
reducing overall production costs and time.
High
Durable
The design of
fixtures that can be used repeatedly and for a longer duration makes it a
durable testing process.
No
Need for Manual Process
It reduces manual
testing and labor, resulting in low chances of human error.
Bed
of Nails Test Fixture in PCB Testing
1. Why use bed of nails
test fixtures in PCB?
Testing
Point easy access: The nails connect
directly with the testing points on the board, eliminating the need for
additional wiring, which simplifies the inspection process. So make a
simple inspection process.
Variable
design of nails: The nails are
designed to be easily customized according to the testing points, ensuring
optimal connections to the board. Hybrid flying probes are used for such
configurations.
Opens/Shorts
Circuits: The spring pin array
helps to check the current flow in the circuit and find any short or open
components on board, as well as solder bridges.
2. How Do Bed of Nails
Fixtures Operate in PCB Testing?
First, the PCB is
placed in the testing fixture, and a button is pressed to lower the
mechanical hood onto the fixture using a pneumatic slide. Electrical probes of
the hood make a connection with the PCB board, and with the use of the
testing sequence board, automated tests started. With the use of
high-speed data acquisition, testing data is recorded. And the report of
the test has data for the pass or failure of the test.
3. Customization of Bed
of Nails Fixtures
The design of
nails for bed fixtures is such that their functions can be set according to
board design requirements. If the board design needs low or high pins, you can
easily modify the pogo pin numbers according to the design. It also has
features for removing the testing points if needed for some boards.
|
Aspect
|
Bed of Nails Test
|
Flying Probe Test
|
|
Testing Method
|
Uses a fixed array of probes to contact test points on the PCB
|
Uses a few mechanically controlled probes to test PCB points
|
|
Speed
|
Suitable for high-volume production; fast testing
|
Slower testing, suitable for low-volume or prototype designs
|
|
Cost
|
High initial fixture cost, but low per-board testing cost
|
Low fixture cost, but higher per-board testing cost due to longer time
|
|
Flexibility
|
Fixed test point layout, not suitable for frequent design changes
|
Highly flexible, easily adapts to different designs
|
|
Testing Precision
|
Lower precision, mainly detects shorts and opens
|
Higher precision, capable of measuring resistance, capacitance, etc.
|
|
Application
|
Ideal for mature designs and high-volume PCB production
|
Suitable for prototype designs, small batches, or design validation
|
|
Mechanical Damage
|
May cause slight dents or mechanical damage to the PCB
|
Almost no mechanical damage to the PCB
|
|
Automation
|
Suitable for automated mass production testing
|
Less automated, often used in lab testing
|
PCBasic's
PCB Test Fixture
PCBasic's test
fixture is customized according to the unique requirements and parameters of
products. It helps to make reliable and strong connections with testing pins
and provides accurate and effective testing results. With the creation of such
fixtures that are according to certain layout and board functions, PCBasic
helps to get error-free results for tests. As a result, you can get
high-quality and rapid production of your products.
PCBasic comes with
fixture services for prototype PCB assembly and large electronic projects. We
do not compromise on high-quality standards for each product or component.
Conclusion
Although there are
many tools and instruments used in PCB manufacturing and testing, the bed of
nails test fixture remains a crucial tool. It offers unique testing and design
features that help to make reliable and high-quality boards. So it is mostly used
for processes where high accuracy and reliability are needed. This technique is
also helpful for providing low-cost testing features and reliable products. It
is mainly used in in-circuit testing to check the components connected on the
board without disconnection and make sure that all components are working well
and do not have any short circuits or open circuits. Additionally, it can be
used to perform various tests, including isolation, resistance, and continuity
tests on the board.
FAQs
1. How does the setup
of the bed of nails enhance PCB testing efficacy?
This PCB testing
increases the efficiency by providing high-speed detection of faults and
correction of these errors on board. It provides accurate results.
2. How often should
fixtures be maintained, and what does it involve?
Do a proper
inspection of the fixture to avoid wear and corrosion, and clean pins regularly
to make strong connections during the test. Normally, pogo pins handle 100,000
compression cycles when needed to be replaced with a new one.
