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Industrial Applications

Introduction

Electrostatic Discharge (ESD) and Overstress (EOS) are serious problems in the semiconductor, circuit board assembly, and electronic-industry in general. ESD/EOS causes damage ranging from immediate failure to performance degradation and shortened lifetimes of all types of electronic products. Moreover, electronic components become more sensitive to ESD/EOS with miniaturization and the ESD Association predicts that this will limit miniaturization if new technologies to monitor and control ESD/EOS do not appear in the next 5 to 10 years.

Commercially available sensors are inadequate to monitor the buildup of charge that leads to ESD/EOS because they are not sensitive enough. Indeed, current sensors are not sensitive enough to measure charging before ESD/EOS occur and damage electronic products during manufacturing. This happens because they can only measure DC fields at short distances (a few cm) from the sensor. Because of this constraint, current approaches to ESD/EOS control are preventive only. Wrist straps, conductive clothing, and conductive floors are used in most manufacturing environments. Nevertheless, wrist straps and conductive strips frequently become loose or detach leading to ESD/EOS damage. These damages could be prevented if a means of monitoring a work area for potentially damaging charge accumulation existed.

The UM E-field sensor mounted inside a PCB assembly machine.

The UM E-field sensor is sensitive enough to monitor potentially damaging charges a few meters from charged objects. In contrast with all other sensors on the market, the UM E-field sensor not only measures the magnitude, but also measures the direction of the electric field (see Table below). This enables users to monitor assembly machines or work areas and take corrective actions long before threshold electric fields large enough to cause damages are reached. Prototypes sensors have been successfully tested at UM and at various industrial facilities. In a head-to-head comparison with commercially available products, the UM E-field sensor outperformed existing sensors in detecting the accumulation of charges in PCB assembly machines even when all sensors are placed within a few inches of the PCBs. Perhaps even more importantly, contrary to other sensors the UM E-field sensor did not produce any false alarms.

Company

Device

Range

Resolution

Accuracy

University of Michigan2-dimensional0 to 106 V/m< 1 V/m< 1 V/m
Company A 1-dimensional0 to 2 x 105 V/m3 to 30 V/m > 60 V/m
Company B1-dimensional0 to 2 x 106 V/m> 1 V/m50 V/m
Company C 1-dimensional Not capable of measuring static fields
Company D 1-dimensionalNot capable of measuring static fields
Company E 1-dimensional 0 to 3 kV at 3 cm 0.3 V at 3 cm 0.1 %
Company F 1-dimensional 0 to 20 kV at 3 cm1 V at 3 cm 5 %
Company G1-dimensional0 to 20 kV at 3 cm 1 V at 3 cm2 %



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