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| Wednesday, October 31, 2018 |
What does a memory tester test?
Memory testers are designed to detect two types of faults that affect the functional behavior of a system ( memory chip, logic chips or PCB board). They are
- Non-Permanent faults
- Permanent faults
Non-Permanent faults occur at random moments. They affect a system's behavior for an unspecified period of time. The detection and localization of non-permanent faults are extremely difficult with a memory tester. Sometimes non-permanent faults will not affect the system's operation during testing.
There are two types of non-permanent faults :
- Transient fault
- Intermittent fault
Transient faults are hard to detect, and there are no well defined faults to detect. Errors in ram introduced by transient faults are often called software errors, the following examples are possible factors that will contribute to transient faults :
- Cosmic Ray (UV light)
- Alpha Particle (Dust)
- Pollution
- Humidity
- Temperature
- Pressure
- Vibration
- Power Supply fluctuations
- Electromagnetic interference
- Static electrical discharges
- Ground loops
Intermittent faults are caused by non-environmental conditions such as:
- Loose connections
- Deteriorating or aging components
- Critical Timing
- Resistance and capacitance variation
- Physical irregularities
- Noise (noise disturbs signals in the system)
Permanent faults affect the logic values in the system permanently, these faults are easier to detect using a memory tester. Examples include:
- Incorrect connections between ICs, boards….etc (e.g. missing connections or shorts due to solder splashes or design fault)
- Broken component or parts of components
- Incorrect IC Mask, (Manufacturing problem)
- Functional design errors (logical function that had to be implemented, is designed incorrectly.
In conclusion - Transcient and Intermittent faults are the most difficult fault to capture even using the today's most sophisticated memory tester, and that is why memory tester equipment manufacturers are continuing to further develop better test algorithm and add on new test features to capture this type of failures. Most memory tester available in the commercial market today - are able to detect most - Permanent faults, when you purchase a memory tester ask the manufacturer for a good explanation on test coverage.
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