Electrostatic discharge (ESD) and automated handling processes
Figure 2. Generation of charges on an IC (ESD) in a transportation system. Figure 3. Charge and discharge of an IC (ESD) in a pick-and-place system.
Figure 4. Example of an FICBM construction
9
. Figure 5. Example for the test of customer PCBs
9
.
model), are not enough to describe ESD is not important, until now. An electrical influence to the process should be tested.
failures. There will be some breakdowns field is able to produce electrostatic charges The measurement constructions served the
caused by humans, but most ESDs are on a PCB, as demonstrated. These electro- static measurement of electrostatic charges
moved in automatic handling equipment static charges will be stored by the bigger on ESDs and PCBs. They were also used
with no direct influence by humans. The capacity of the PCB or by the electronic for the limit proof of measurement devices
electronic components and assemblies components on it. The discharge process and the specification of new requirements
charge themselves electrostatically, and the is not predictable. It can happen when to these devices.
capacity conditions of a PCB are absolutely the PCB is grounded or contacted. That’s The present standardized measure-
different in comparison to humans. The why the description of FICBM is not easy, ments only demand a check of whether the
value of the capacity is higher than the but the effect is very important. Electrical machine is grounded and that all used ma-
body of the person. The result is a bigger fields can appear everywhere, where ma- terials are not electrostatically chargeable—
electrostatic charge on the board. We have chines or motorized plants stand or where the actual process won’t be tested. The
a bigger energy at the discharge. Damage circuit processes are produced. fact that the actual process is very dynamic
to ESDs is more severe. That’s why a new and fast makes all the more difficult. The
model has been searched for for some Measurement methods present ideas about the measurements have
years. One solution is the charged board The previous experiences demonstrate that to be checked and completed. Addition-
model (CBM), which simulates a charged measurements of real electrostatic charges ally, there are no absolute failure models.
PCB. are not so simple. Measurements can only At the moment we have the normal CDM
be made when the machines stop, so only and the future FIM. These combinations
2. FICBM static measurements can be realized. But of failure models, especially the FIM,
A different model is the field-induced experience shows that the act is complex. are not explainable very well. The other
charged board model (FICBM). The influ- First tries were realized with different failure models, CBM and FICBM, have
ence of the electrical field on PCBs has measurement constructions. Thereby typi- to introduce in the future reflections and
been neglected or has been thought that it cal measurement construction and their adjustments.
Continued on page 19
14 – Global SMT & Packaging – January 2009
www.globalsmt.net
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