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www.us- tech.com


September, 2019


Mitigating ESD Risk in Barcode Labeling and Masking


By Tom Rogers, Technical Director, Cindy von Recklinghausen, Senior Product Manager, and Emily Heisig, Product Manager, Polyonics P


CB designs are becoming smaller and more complex every day, with layers of circuitry and components, which makes manufactur- ing and assembling them increasingly difficult. It


ESD can also result in latent defects, resulting in reliability concerns. There are many components on PCBs that


are vulnerable to ESD, including microcircuits, discrete semiconductors, thick- and thin-film resistors, and piezoelectric crystals. Pre - cautions are needed in order to prevent dam- age from an ESD event. ESD damage can be seen immediately during assembly when a cir- cuit stops functioning, or later during the use- ful life of the device. This latent ESD failure


adds to the “cost of ESD” with repair costs, return costs, and end-user disappointment. The industry has estimated that product losses due to ESD can be as high as 7 percent.


Magnified images showing ESD damage on a microcircuit.


is imperative that PCBs are designed to meet their intended uses and operate flawlessly under adverse conditions over their entire lifetimes. Meeting these objectives and mitigating risk requires manufacturers to design a device or PCB that can survive or tolerate an electrostatic dis- charge (ESD) event. The ESD problem in electronics production


and especially PCB assembly is significant. An ESD event can cause physical damage (e.g. surface oxidation and material loss) to circuits — either printed on the PCB or embedded in a component.


Understanding Static and ESD


The main source of static


comes when two dissimilar sur- faces are brought into contact and then separated. The charge imbal- ance, or triboelectric charge, on each of the separated surfaces creates an electrical potential that may enable that charge to move. In PCB assembly, there are several key


Tables 1 and 2: CDM (left) and HBM (right) ESD component classification levels.


human and components may react differently to the discharge rates. As an example, a CMOS component may have


processes that create a triboelectric charge. They include human contact, machine contact (convey- ors, robotics, etc.), component mounting, applying solder paste, tape masking and barcode labeling. All sources require consideration when developing


an HBM sensitivity of 1,000V, but only a 500V CDM. PCB and component manufacturers may use the ESD threshold classification to character- ize their part. Tables 1 and 2, used in the


Continued on page 68


an ESD control program. Component manufacturers provide data for


ESD sensitivity levels and characterize the sensi- tivity based on exposure to humans and machines using the human body model (HBM) and charged device model (CDM). The main difference between the two models is the rate of discharge, with the human body releasing charges slower than when metal-to-metal contact occurs in CDM events. Even if humans and machines have the same 5 kV potential, the rate of discharge is slower from the


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