Fixtureless In-Circuit Test
Encyclopedia
Fixtureless in-circuit test (FICT) is a cost-effective alternative to a "bed of nails" tester for in-circuit testing of low to medium volumes of printed circuit board
assemblies. It relies on a computerized optical inspection of the circuit assembly and positionable test probes. Traditional "bed of nails" testers require the manufacture of a complex mechanical fixture comprising pins inserted into holes in an acrylic plate connected to the measuring unit by wires. Some of the disadvantages of the bed of nails tester is the number of wires used will often increase the capacitance
of the circuit so that values below 60 pF are difficult to measure accurately. Also, the holes in the plate do not allow pins to be placed close enough together to test fine pitch components with a lead pitch of 0.5 mm unless test pads or via
s allow connection from another part of the circuit.
Typically, four to six weeks are required for the manufacture and programming of a bed of nails fixture. Fixtureless In-Circuit Test does not suffer from any of these drawbacks and, in combination with smart software, testing can be done within hours for a low complexity design and within a few days for the most complex designs.
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
assemblies. It relies on a computerized optical inspection of the circuit assembly and positionable test probes. Traditional "bed of nails" testers require the manufacture of a complex mechanical fixture comprising pins inserted into holes in an acrylic plate connected to the measuring unit by wires. Some of the disadvantages of the bed of nails tester is the number of wires used will often increase the capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
of the circuit so that values below 60 pF are difficult to measure accurately. Also, the holes in the plate do not allow pins to be placed close enough together to test fine pitch components with a lead pitch of 0.5 mm unless test pads or via
Via (electronics)
A via is a vertical electrical connection between different layers of conductors in a physical electronic circuit.- In IC :In integrated circuit design, a via is a small opening in an insulating oxide layer that allows a conductive connection between different layers. A via on an integrated circuit...
s allow connection from another part of the circuit.
Typically, four to six weeks are required for the manufacture and programming of a bed of nails fixture. Fixtureless In-Circuit Test does not suffer from any of these drawbacks and, in combination with smart software, testing can be done within hours for a low complexity design and within a few days for the most complex designs.
Benefits of fixtureless in-circuit test
- Automatic optical inspection for presence of components, correct polarity, and letters or numbers on ICsIntegrated circuitAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
. - Value measurements on resistorResistorA linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
s, capacitorCapacitorA capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
s, Zener diodeZener diodeA Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
s and inductorInductorAn inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
s. - IC open circuit checker finds lifted legs and dry joints on ICs.
- Can test fine pitch printed circuit boards down to 0.3 mm with a repeatable accuracy of probe placement of ±0.05mm.
- Test program is rapidly prepared from printed circuit board CAD data.
- All major CAD platforms support FICT.