ESD / EOS
failure prevention methods
The work environment is the most basic and the most important factor for preventing ESD failure. ESD failure caused within the work environment can be controlled by the use of a grounded mat or wrist straps. If it is difficult to apply grounding to the work area, you can neutralize the charge within the air by using an Ionizer.
| D-generating activities | Source of ESD |
|---|---|
| Can be generated during all activities | worker |
| clothes made from synthetic fibers, non-conducting shoes | clothes |
| waxed chair | chair |
| un-grounded or waxed work table | work table |
| direct contact with the IC | worker |
Take appropriate measures to prevent the interaction of charged objects and to minimize the shock during discharge.
Grounding the Worker and ToolsThe tools must be grounded, and the worker must wear a wrist strap and observe Heel grounding.
Grounding the Work TableUse appropriate resistance to the work table (ESD Limiting protective resistance) for grounding.
Places where ESD is concentratedUse an Ionizer to neutralize the charge within the air in areas with concentrated ESD failure.
EnvironmentHumidity is another factor which influences electronic transfer between charged objects. If the humidity is about 10-20%, the possibility of ESD failure and the ESD level is heightened. The possibility is lowered between 65-90%, but Corrosion-related failures may occur instead. Therefore, it is very important to maintain appropriate humidity levels (normal: 45~55%).
EOS failures may occur when a non-standard or an incorrect operation method is used. It is important to standardize the Testing and Operation methods, and to use a stable power supply method to prevent EOS Surges. The most common EOS Failures are caused by inserting or separating an IC without first turning off the System Power.
| Causes of EOS generation | Preventative Methods |
|---|---|
| Non-standard testing method | Documentation of the testing method |
| Unstable power supply | Stable Power Supplier |
| Inserting while Power is On | Inserting only when Power is Off |
| Poor board layout | Ensuring enough margin for layout |
Minimize the factors causing EOS-related Surges on the semiconductor.
Surge in the Power SupplierUse a stable power supply and monitor regularly
Separating the IC when power is onSeparate the IC only when the system and board power are off (Hot switching insertion).
Poor ConnectionRegular inspections of the areas with poor connections, and education of the workers.
PCB Layouts that are weak towards EOSSeparate the signal and power line when designing the PCB layout pattern
Grounding of Test ToolsRegular inspection of grounding status.
Input Signal & Power application orderDocumentation of the Power application order, and education of the workers.
IC inserting direction during TestingBe cautious of the IC direction during board insertion.
| Check Item | Standard |
|---|---|
| Temperature of work area | 23 ± 4 |
| Humidity work area | 50% ± 5 |
| Temp. control cycle | 1/week |
| Work table grounding | Grounding check |
| Work table Cleaning | Cleaning check |
| Work chair grounding | Grounding check |
| floor matter | Conductive matter |
| floor Cleaning | Cleaning check |
| Check Item | Standard |
|---|---|
| cloth | Conductive matter |
| wrist strap | Used wrist strap |
| Wrist strap resistance | 1M Ohm check/day |
| shoes | Conductive shoes |
| Shoes outsole | Cleaning |
| Handling Box | Antistatic meter |
| Work area electromotive | Grounding check |
| Conveyer belt | Grounding check |
| Check Item | Standard |
|---|---|
| Main Power Monitoring (AC) | EOS Surge check |
| Power Supplier Monitoring | EOS Surge check |
| Power Supplier | Calibration |
| Test sequence | Manual |
| Test method | Manual |
| Worker training | 1/month |
| Jig Connector | Check |
