In-Circuit-Test

The In-Circuit Test (ICT ) is a testing method for electronic components or circuits (german electrical circuit ) and assembled printed circuit boards in the electronics manufacturing. When ICT is the examination of the component parameters of an assembled module or the electrical connections of a circuit board in the foreground.

In this case, the printed circuit board after it has been placed on or in a special test adapter, for errors in the conductor track routing ( such as short circuits or open circuits ), solder defects and error components tested. And all the circuit blocks (clusters) can be tested.

The ICT test system analog components parameter (resistance, capacitance, inductance, etc.) measure different measurement methods (for example, two-wire, four-wire measurement, etc. ). For the verification of digital components defined test signals can be fed and their effects can be measured.

If an ICT test system is limited to the measurement of analog components, we also speak of an MDA ( manufacturing defect analysis).

  • 3.1 Measuring voltages and currents
  • 3.2 Measurable sizes for components
  • 3.3 Tolerances of measured variables
  • 3.4 Non- or not properly measurable parameters in components
  • 3.5 Further measurements

Test strategy

The test of printed circuit boards is usually carried out immediately after production of the printed circuit board, or immediately before the loading of the printed circuit board. This is usually a Go-/NoGo-Test, wherein the faulty circuit boards are discarded.

The ICT test of loaded assemblies can be performed directly after the last placement and soldering step, even before the assembly is subjected to a functional test for the first time or the assembly is placed on the operating voltage. When ICT test of the assembled modules a Go- NoGo test is also carried out, where the error can be displayed in non-functional assemblies. In the assembly can be repaired this error, such as device errors, missing solder joint or solder bridge between two adjacent networks. ... Then the assembly is tested for the detection of a successful repair again.

The situation is different in the functional test of an assembly in which the total or partial function of the circuit is in the foreground and less measuring individual component values ​​. If a test function integrated in the ICT, this is often only a certain part of the overall circuit function in focus.

Sometimes the program components of the assembly or the use of boundary-scan is also performed in the ICT test.

Adaptation of the module

Feeding or handling the modules

The supply of printed circuit boards or assemblies to the test system can be done through different variations:

  • Manually is useful especially with long test times or smaller series
  • Feeding from the magazine, for stand-alone machines
  • Feed from trays, stand -alone machines
  • Inline system, especially in larger series for linked process steps
  • Feeding in workpiece carriers which can be delivered from magazines or from an in-line system.

The magazine and tray handling can be optionally integrated in the machine or implemented with a built handling system.

Contacting the electrical networks

The electrical networks are contacted by an adapter. For contacting special spring-loaded pins are ( also referred to as test needles ) used with a variety of head shapes. This meet certain solder - free areas on the board, the so-called test points. The contacting can be constructed with a variety of adapters and Kontaktierarten. Frequently contacting with the support of a vacuum or compressed air takes place. The vacuum fixture, the assembly is pressed by the negative pressure against the needle bed, for example. Also, a purely mechanical clamping of the printed circuit boards or modules is possible.

The contact with an assembled module can be done in two different ways in principle. In the first case, the soldering of the assembled components or the components can be contacted by the needle. In the second case, additional test points are on the board of the assembly included. It is rectangular, square or round copper surfaces without solder mask that can be used for contacting. As in the first method and the soldering parts can be damaged, if necessary, in general the method is used with additional test points.

When considering a bare board, the contact points of the components to be soldered can be contacted directly as a test contact with.

Adapter types

It can generally be distinguished test fixtures between two varieties: spring pin and rigid needle adapter.

Spring pin adapter

This adapter is used in most of the ICT test systems. The test points and component pins can be contacted and measured directly with spring contact pins. In practice can be realized with this Kontaktierabstände contacting system of 0.8 mm. Through the swash game of the spring pins but should the test areas have at least a diameter of 0.6 mm. But special additional process and design features also allow smaller test areas and contact intervals, thereby the bonding force, and the life of the spring contact pins is reduced. In the mass production test point diameter be 1.0 mm or larger is used to minimize problems due to measurement errors, and thus the necessary contact rework.

The spring pin adapter can be distinguished in vacuum adapter, pneumatic adapters or mechanical -contacting adapter.

The rigid needle adapter is mainly used when (> 0.2 mm, Kontaktierabstände > 0.25 mm test points) to be contacted on very small structures or an adapter with a very long service life is desired. Due to the complex structure they are more expensive than a spring pin adapter, but this extra investment is worth quite fast, since much less servicing and related system downtime incurred. The full benefits of this adapter but can only be realized if the position of the substrate is detected optically by the ICT test system, and a position correction in X, Y and θ is performed.

Other adapters criteria

At appropriate positioning of a circuit board in relation to the ICT needle bed two asymmetrically arranged PCB holes ( rotation) should be present in the test specimen or benefits. It is then in the needle bed, two so-called positioning introduced to bring the printed circuit board in accordance with the optimum inspection position.

In general, make sure that the candidate is not bent and damaged so that by the force of the needle bed adapter ( test needles, points of support, pressure pads, etc.). It is accordingly sufficient to support the circuit board contact points but also as a counterpart to the probe needles corresponding number of hold-down for optimum clamping of the printed circuit board to provide to the needle bed.

While a positioning of the specimen beyond the outer contour of the specimens or benefit is also possible, but it brings a greater positioning inaccuracy with it (eg by dirty partitions of the circuit board ). It must then be dimensioned correspondingly greater on the test specimen, the test points. Furthermore, care must be taken at a Konturklemmung that the candidate has a certain stability so that it can be clamped at all (especially with modules without margins ).

Assembly for single-sided contacting

Assigns the circuit board test points only on one side and is airtight, so it can be sucked with a vacuum table and a suitably adapted negative seal. Assigns the examinee many holes on or you want to save the special preparation of a seal, a vacuum adapter is provided with a hood. In the hood appropriate hold-down must be provided. The PCB should thereby be taken out and about positioning.

Assembly for double-sided contacting

Must circuit boards can be contacted on both sides with needles, so you can not work with a vacuum seal. At a vacuum adapter then a hood adapter is build with integrated second needle bed and hold-downs or a purely mechanical adapter with lower and upper needle bed. The circuit board must have positioning for needle bed are centered and also the upper needle bed must be centered with the bottom to ensure optimal contact is ensured.

Single-stroke system

When Einhubsystem the contacting operation takes place with a stroke, that is, the circuit board is positioned in the contact system and the adapter shuts down the circuit board. Take the test pins to the circuit plate, is built with the remaining stroke of the necessary bonding force.

Zweihub system

A Zweihub or Doppelhubsystem is used when you are not allowed to contact the test specimen with the full needle bed to perform a specific ICT measurement. For this test needles are used with different lengths. Only the longer contact probe needles the samples in the first stroke. In the second hub contact short and long test pins on the UUT. A good example of application is to perform the ICT in complete contact needle bed and then perform with reduced needle contacts a small additional function test and programming of components.

Single chamber or dual-chamber adapter

The various ICT test systems often offer the opportunity to build even a so-called dual-chamber / dual-chamber adapter for the assembly. As a result, the processing time for loading a module in a test chamber to be completely eliminated from the test period, while the test system checks the module in the other chamber.

Measured variables

Measuring voltages and currents

The analog component measurements at ICT testers are typically carried out with low voltages and currents. By default, in this case are in the range of voltages of 0 V to 1.0 V is used. The measurement currents are typically in the range of a few microamperes to a few milliamperes. Larger measuring voltages are often not allowed at assemblies. There is always the risk that other components can be damaged by the test voltage or diode paths are conductive, so that can not be measured reasonably within the circuit of an assembly. For the same reason, the maximum measuring current is also limited because the current carrying capacity of wires on the circuit board or the components limits the maximum measuring current in very unfavorable circumstances. In the ICT test systems for the measurement of resistance values ​​is typically used, a DC voltage, an AC voltage while commonly used in capacitors and coils.

Measurable quantities in components

Most ICT test systems can typically perform the following measurements analog components.

Tolerances of the measured variables

The side to be measured devices have all tolerances. For example, consider the tolerance limits of an electrical resistor with a nominal value of 10 k at room temperature and a tolerance of the resistance value of ± 1% of nominal. The actual resistance value can thus be between the lower limit of 9.9 kOhm and 10.1 kOhm. The ICT test system is also non-zero fault tolerant and therefore this tolerance must be added to the actual component tolerance will be added. Does the ICT test system so for example for a measurement of a resistance in the range 10 k, a measurement tolerance of ± 0.8%, it must in this case, the measuring range for the test of the resistance with a lower limit of 9.82 kOhm and the upper limit be set to 10,18 kOhm.

Not or not properly measurable parameters in components

Various electrical parameters can not or ICT test systems can not be detected correctly.

(VDR resistors)

Other measured variables

Larger ICT test systems, in addition to the pure analog component test often also the test assembly with power supply and carry out further tests. The field ranges from simple digital ICT, stimulated at the input pins of a component and the expected signals are observed at the output pins of the device, up to the ( extensive ) function test.

Typical test sequence

  • Unload routine, especially the unloading of electrolytic capacitors (used for security on board and test system as well as for measuring stability, this step is always performed as a first step )
  • Contact test ( to check whether the test system is properly connected to the module)
  • Short-circuit test (test for solder defects )
  • Analog components test ( test of all analog components for the presence and value)
  • Testjet ( Agilent), frame scan ( Genrad / Teradyne ), QTest2 sample ( Aeroflex ) or Electro Scan ( SPEA ) (Comparative Test of ICs for the presence and correct soldering )
  • CODA - test ( Aeroflex ) (test for correct polarity of capacitors )
  • Supply assembly with operating voltage
  • Powered analog test (test of analog components, the need for the operating voltage, e.g. relay )
  • Powered digital test (test of digital components: stimulation of input pins, monitors the output pins; comparison with nominal values ​​)
  • Boundary scan test
  • Flash, ISP and more component - programming
  • Agilent Medalist Beadprobe - bead probe technology
  • Agilent / Teradyne Powered Vectorless Test Solution - VTEP v2.0/Powered FrameScan
  • Take assembly of the operating voltage
  • Discharge routine to pass module voltage neutral ( as in the beginning ).

While most typical ICT test systems have the appropriate equipment in the system, to perform the tests listed above, additional hardware components are available for special supplementary examinations often necessary:

  • A camera system for checking the presence and polarity of otherwise measurable components
  • Photodetectors for testing LED color, intensity, homogeneity
  • External frequency measuring devices for testing of very high frequencies
  • Additional Equipment for measuring signal analysis such as slope, envelopes ( FA08 map Aeroflex )
  • External equipment for high-voltage measurements (eg,> 100 V DC) or alternating voltage sources.

Other Test Equipment

Here are a few more test techniques often found in the manufacturing process of electronics production application:

  • AXI Automated X-ray Inspection
  • AOI Automatic Optical Inspection
  • FKT function test / final test
  • Boundary-scan technology.
In-Circuit-Test Functional Testing (manufacturing) Standalone software
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