Electrostatic discharge (ESD) and automated handling processes
1. Removal of ESDs from packaging. for electrostatic charges. These charges ESDs from one station to another. Figures
The ESD has an isolating case, so are great and dangerous potentials for 2 and 3 show this situation.
it will be electrostatically charged ESDs, and are independent from humans. All these acts show damage models.
during removal from the reel or Every movement of ESDs in automated ESDs will be electrostatically charged every-
the tray. pick-and-place machines is enough to where, for example, when they are grasped
2. The electrostatically charged ESDs create very high electrostatic charges. The from trays or reels. After grasping them,
will be transported to the PCB. newest reports confirm this
3, 13, 14
. PCBs are they are transported with the electrostatic
The movement of a high-speed usually made of isolating plastic material charge to the PCBs, because ‘pick and
pick-and-place system generates that generates electrostatic charges. It is place’ doesn’t guarantee a safe discharge.
further electrostatic charges. not enough to ground the copper bands The PCBs are always made of isolating
3. When an ESD is placed on the for discharging the plastic surfaces. The material, so they can also be charged with
PCB, the difference in potential be- electrostatic charges on PCBs can’t flow to their own potential. The ESDs are placed
tween the two leads to a discharge, the copper bands for discharging over the on and the charge compensation happens.
which will damage the ESD. metal parts. The plastic material of PCBs is The discharge current leads to damage of
not conductive. ESDs lay in trays or reels, the ESDs. The PCBs will be electrostatical-
These examples show that electrostatic
and when they are grasped, the charges are ly charged during the transport to the next
charges always develop when ESDs are
parted and an electrostatic potential is gen- station or during the production process.
parted or moved. Electrostatic charges will
erated. Basically electrostatic charges always There are different proposals for the
always generate because components and
arise because the case material of the ESDs replication of discharge models. Among
PCBs are made of an isolating material.
is not conductive and the packing (trays or other new models, the so-called CBM
The pick-and-place process is not the only
reels) is made of material that is sometimes (charged board model)
9, 10, 11
or FICBM
possibility for the generation of electro-
conductive, but in most cases don’t meet (field-induced charged board model) is
static charges in a production process. The
static control requirements. When conduc- suggested.
printing of PCBs, the labelling of PCBs
tive reels are used, covered with non-con- These examples show that the ap-
and assemblies, and the testing of assem-
ductive tapes, a high electrostatic charge proach for the test of electrostatic charge in
blies are other critical steps.
arises when the tape is removed. Another connection with PCBs is very complex.
esD and machines, measurement
problem is the fact that the reel or the
methods, protection concepts
strap, where the ESDs lie, is not a Faraday Failure models
cage. The ESD is not protected when it is 1. CBM
Extended tests in different production
carried out of the EPA. The previous models, HBM (human body
processes show that machines and produc-
A further case means the transport of model) and CDM (charged device
tion plants, as well as PCBs, are sources
Figure 1. Development of the sizes of ESDs and the ESD sensibility through 2020
12
www.globalsmt.net Global SMT & Packaging – January 2009 – 13
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