In-Circuit Testing for PCB Assemblies
Component-level electrical checks within your PCBA build.
FLJ provides in-circuit testing as part of PCB assembly. Board-specific contacts and test programs support selected connection and component checks, with fault investigation and relevant retesting after corrective work.
Electrical Checks on Assembled PCBs
Opens, Shorts and Component Measurements
FLJ tests selected connections and component paths against limits set for the assembled circuit. The program applies a suitable electrical stimulus and measures the response through the fixture contacts.
Scroll the table to read all three columns.
| Siehe | Electrical observation | What it helps investigate |
|---|---|---|
| Continuity of an intended connection | Whether the selected nodes show the expected conductive path | An open connection, missing part, or other interruption along that path |
| Isolation between a selected net pair | Whether conductance between nets expected to remain separate stays within the programmed limit | An unintended conductive path, contamination, or a connection needing closer inspection |
| Resistor or capacitor path response | Resistance or a capacitance-related response under the measurement conditions defined for the circuit | A missing or wrong-value part, or a connection that changes the expected response, where the circuit makes it distinguishable |
| Suitable semiconductor junction | Junction response in the direction or directions specified by the check | A possible polarity, placement, or device-path issue for investigation |
An out-of-range reading identifies a check to investigate. Unexpectedly low resistance between nets may suggest an unintended connection, but the reading alone does not locate a solder bridge or establish its physical cause.
How the Surrounding Circuit Affects a Reading
A component remains connected to its neighbouring circuitry during an in-circuit measurement. Current can divide between available paths.
In the illustrated circuit, both 1 kΩ resistors share nodes A and B, so a measurement across A–B sees their 500 Ω combination. Reaching both ends of either resistor leaves it connected to the second branch.
An appropriate guard drive can reduce the voltage difference across part of an alternate branch, limiting current diverted from the measurement source. It requires an additional accessible node, suitable circuit topology and a supported test setup. The directly parallel pair shown here has no intermediate node for that control.
Bed-of-Nails Fixtures and Test Access
For repeatable ICT, FLJ matches the fixture’s contact layout to the selected nodes on the assembled PCB.
A bed-of-nails fixture holds the board while spring probes meet exposed test pads. Its wiring carries the selected nodes to the test system, so the physical interface follows the connections used by the program.
Positioning and support matter when several probes contact the board together: they help limit board deflection and changes in probe engagement. A point visible in CAD may be blocked by a populated component, or its solder-mask opening may not provide usable contact. The suitable probe approach and the board’s actual assembly stage therefore shape which locations can be reached. Test-point and fixture access can also be considered earlier through design-for-testability planning.
Probe-to-pad contact resistance can contribute to the measured value, particularly in low-resistance checks. Changes in contact engagement can therefore produce changing readings even before a board fault is considered.
Test Programs, Fault Diagnosis and Retesting
Board-Specific Test Programs
FLJ sets up the test program for the released board revision, connecting selected node and component references with the measurement conditions and acceptance limits. Fixture wiring, node mapping and the program must correspond, so each reading belongs to its intended circuit path.
A component substitution or configuration change can alter the expected response even when the test points stay in place. Those changes need to be reflected in the program used for that build.
Investigating a Failed Measurement
FLJ investigates a failed check through its mapped network or component path. The contact and fixture connections are checked alongside the program conditions: a worn probe, broken or miswired connection, or incorrect node mapping can produce an abnormal response. Once that measurement path is established, investigation can focus on the affected circuit and assembly location.
Where an assembly fault is confirmed, we correct the relevant connection or component location and repeat the affected programmed checks. The specified test records can identify the build, check and finding, with any required retest results.
ICT Fault-Diagnosis Examples
A failed electrical check becomes useful when it points to a circuit path to investigate. These examples show how FLJ approaches fault investigation and relevant retesting within a PCBA build.
Illustrative diagnostic examples. The photographs show reference soldering defects, not FLJ customer projects or recorded ICT results.
A Connection with an Intermittent Open
- Electrical symptom
- A path expected to conduct measures high resistance or intermittently fails its programmed continuity check.
- Investigation
- Confirm probe contact and fixture wiring, then inspect the mapped lead, solder joint and copper path. A cracked joint can interrupt that connection; a static check may still pass while the crack is closed.
- Correction and recheck
- Repair the confirmed joint fault and repeat the affected checks. An intermittent fault may require additional verification under the conditions in which it occurs.
An Unintended Connection Between IC Leads
- Electrical symptom
- A selected pair of nets expected to remain separate shows conductance above its programmed limit.
- Investigation
- Verify node mapping and the fixture path, then examine the affected circuit. Excess solder between adjacent leads is one possible cause when those leads belong to separate nets.
- Correction and recheck
- Remove a confirmed unintended bridge, inspect the disturbed leads and pads, then repeat isolation and the relevant connection checks. A cleaner-looking joint alone does not establish an electrical pass.
FLJ combines electrical findings with optical inspection of visible assembly features, corrective assembly work and relevant retesting.
ICT in Production PCB Assembly
Preparing a dedicated fixture and program creates a repeatable physical and electrical setup for an unchanged board revision. The same contact interface and defined checks can then be used across successive units and repeat lots, spreading that preparation effort over the build rather than creating a new setup for each board.
That benefit depends on repetition of the relevant design. Changed contact positions or expected responses can interrupt reuse, so production quantity, revision stability and the required checks belong in the choice of test method. Programmable flying-probe systems offer moving contacts for smaller or frequently changing builds; the choice follows the board and production plan.
FLJ supplies PCB assembly and testing with selected ICT incorporated into the production route. Where firmware loading is also needed, in-circuit programming can be coordinated with the build.
ICT verifies the electrical conditions defined by its program. Functional verification exercises specified product responses under operating power, through the required interfaces and test conditions.
Tell us about your board revision, production quantity and the checks you need. Existing test procedures or fixture information can help define the testing for your next build.
Discuss Your PCBA Test