Sources of ESD in a Production Line
It is necessary for everyone who handles ESD sensitive devices to know the reasons for failures. This paper discusses causes for ESD in a SMT production line.
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Authored By:
Hartmut Berndt
B.E.STAT European ESD Competence Centre
Kesslesdorf, Saxony, Germany
Summary
The number of failures caused by electrostatic discharges (ESD) has been increasing for some time now. So, it is necessary for everyone, who handles electrostatic sensitive devices (ESDS), to know the reasons of such failures.
This presentation will give an overview about possible causes for ESD in a SMT production line. Particularly automated production lines have some processing steps, where electrostatic charges are
increasingly generated. So far one has been focused on the human being. This is controllable.
Measurements in production lines show electrostatic charges at the following processing steps: application of soldering paste (printer), assembling (automated and manual pick and place), and labelling as well as optical and electrical tests (ICT). The electronic components are always assembled directly and without any covering on the PCBs. Thus, the wire bonding process leads to a damage of the electronic components.
This process step is a very critical part in the production line. The electronic devices will be directly
contacted with a metal needle. The process steps, where the PCBs are covered with enclosures must be inspected either. Such enclosures are mostly made of isolating materials, like plastics.
Thus, those can be electrostatic charged highly, while assembling. An optimized ESD Control System for machines with the emphasis on cost-effectiveness will be presented.
Conclusions
In conclusion, it can be said, that there are many sources for electrostatic charges in a SMT production line. The different steps lead to high or low electrostatic charge. First measurements were realized to determine the true charge. A great problem is that all machines must be stopped for the measurements. In the future it is very important, that we can measure in a normal machine, while operating.
Presently, the only possibility is ionization. The grounding of all parts does not suffice; it is just a basic requirement. The moving parts CB and ESDS cannot be grounded. Nevertheless, these are the parts, which are electrostatically charged and which cause the damages.
Initially Published in the SMTA Proceedings
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