CHECKSUM Manufacturing Defect analysis (MDA)

CheckSum, manufactures low-cost, in-circuit test (ICT) systems used to detect and isolate manufacturing process faults. CheckSum test systems are used in both low and high-volume manufacturing production lines.

CheckSum provides complete in-circuit test systems for assemblies with single or double-sided surface mount technology (SMT) as well as through-hole components.  CheckSum provides also in-circuit, vectorless test using Agilent TestJet Technology.  Boards with boundary-scan can also be tested using functional in-circuit test (ICT). These systems can include in-system programming (ISP).

Checksum Benchtop MDAMDA Test System CheckSum

Measurement Capabilities
Even though CheckSum MDA systems are truly low in cost compared with alternatives, they provide extremely sophisticated measurement capabilities. You can choose from several basic techniques to achieve the best in-circuit measurement results. Measurements use DC current or AC/DC voltage as measurement stimulus.

Resistance, Capacitance and Inductance Measurements
Current-based measurements are performed by applying a DC constant-current through the component being measured, then measuring the resultant voltage drop. For current-based capacitance measurements, the system measures the rise-characteristics of the developed voltage over time to determine the capacitance value.
DC voltage-based measurements apply a voltage to the component being measured, then measure actual voltage across the component and the current that passes through it.
When AC voltage-based complex-impedance measurements are made, the system applies the signal, then measures the in-phase and quadrature-phase voltage and current. From these, the capacitive, inductive and resistive components of the measurement are determined.
By choosing from alternative frequencies, the impedance of the measured component can be optimized compared to parallel impedances for best measurement results.
In some cases, capacitor polarity can be tested by applying current-limited DC to the capacitor and measuring the voltage across the capacitor. A lower voltage is developed if the capacitor is installed incorrectly.
To eliminate the effects of path resistance internal to the tester and in the fixture wiring, measurement points can be externally sensed, providing 4-wire Kelvin measurement capability at the UUT rather than internal to the tester. This helps increase the accuracy of low impedance measurements.
To prevent semiconductors from turning on during the measurement, you can choose a 20 or 200mV full range stimulus in place of the standard 2V stimulus. AC measurements can be biased to prevent interference from parallel diodes in the measurement path.

Guarding
In-circuit measurements often contain parallel impedances that can cause measurements to deviate from component nominal values.
Guarding provides the capability to minimize the effects for parallel impedance paths. Guarding uses special sense and drive circuitry to source or sink current into other UUT circuit nodes to eliminate current flow through these paths. CheckSum MDA systems allow you to specify multiple guard points during a measurement. Guard points can be externally sensed to provide additional guarding accuracy when low impedance paths exist. With CheckSum MDA systems, any test point can be used as a guard point. No special wiring is required.
Unlike other MDA systems, CheckSum uses separate guard drivers for each of its guard points. This additional sophistication can provide the proper guard voltage at each guard point, regardless of connection impedance differences.
Even without guarding, MDA systems can often directly measure components of different types connected in parallel, such as a capacitor and a resistor, with the use of complex-impedance measurements.

Transistors and FET Testing
Three-terminal devices such as transistors and FETs are tested by measuring between the current-carrying terminals while biasing the control terminal. FETs are biased with voltage, while transistors are biased with current.

Diode Testing
Diodes, LEDs, zener diodes and transistor junctions are tested by applying a constant-current, then measuring the voltage dropped across the device.

IC Orientation and Presence Testing
IC presence and orientation is verified by checking the semiconductor junction voltage of the protection diodes typically present between IC pins and the UUT power supplies. This mapping is self-programmed from a known-good UUT.

Opens and Shorts Detection
Since most faults that occur during manufacturing are shorts, MDAs provide the ability to perform continuity testing for opens and shorts. The systems self-learn the continuity map of a known-good UUT, then test against this map for other UUTs. Selected open/short measurements can be ignored to prevent testing of components near the continuity threshold or to provide better diagnostics with separate measurements.
Using the Agilent TestJet Technology option, CheckSum MDA systems can find open connections to surface-mount technology (SMT) devices such as ICs and connectors.

Relay Testing
UUT relay coils can be controlled for testing contacts in both the normal and actuated positions.

Transformer Testing
Transformer coil presence can be tested with resistance and/or inductance measurements. CheckSum MDA systems can also test the polarity of transformer connections to ensure that they are correct. Since transformers are often hand terminated, this will find faults not detected by normal coil resistance testing.

Digital I/O
Most systems include digital I/O bits (expandable) that can be used for sensor input, control output, or limited digital testing.

TestJet Technology
A common fault in surface-mount technology manufacturing is open connections. On components with bussed connections or high impedance pins, these faults cannot be detected by normal analog in-circuit measurements. The CheckSum TR-8 MDA allows you to detect these faults using the Agilent TestJet Technology option. A flat sensor probe is built into the fixture over each component body to be tested. The system measures from this sensor probe to each signal pin on the SMT device. By measuring precise capacitance values (in the fF region) the system detects open connections. This technology works for most SMT ICs and connectors. The sensor probes can be included in single and dual-sided fixtures.

In-System Programming
Checksum MultiWriter uses proven, patent-pending simultaneous programming technology to program up to 24 parts each of up to 16 different types simultaneously—up to 384 chips at one time—usually in seconds instead of the minutes required by conventional programmers.
MultiWriter uses low cost “universal hardware” and easily configured software. With controller and programming buffers mounted right in the fixture, high signal quality is assured. Comprehensive serial flash and microcontroller library with many supported bus algorithms including I2C, SPI, Microwire, JTAG, and PIC.

System Examples

Checksum Benchtop MDA

Checksum Benchtop MDA

Checksum Benchtop
Flexible MDA system

Checksum Benchtop MDA system with mechanical fixture receiver up to 400 testpoints

Checksum Analyst

Checksum Analyst

Checksum
Integrated MDA – Functional test system with Agilent 3070 style fixture receiver

Checksum
Integrated MDA – Functional test system with pneumatical fixture up to 1000 testpoints

 

 

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