fastening & assembly solutions and technology - Approved Business

FAST OCTOBER 2011
ENCAPSULANTS
The benefits of
low pressure moulding
Traditional methods of encapsulation can result in parts being damaged. Materials expert Jim
Marshall discusses the benefits of using hotmelt resins as an alternative
A typical use of a hot melt resin
is the encapsulation of PCB
boards in various configurations
Traditionally, high pressure techniques
– sometimes up to 200 Bars – have
been used for encapsulating applications,
including the protection of printed circuit
boards (PCB) and moulded connectors.
However, with such heavy pressure,
breakages are commonplace. Indeed,
one PCB manufacturer faced a rejection
rate of 65% because of shortcomings
with this method. However, once introduced
to low pressure injection, where
pressures of just 4 to 12 bar are required,
this same manufacturer managed to
reduce dramatically the rejection rate to
almost nil.
Low pressure moulding is an innovative
manufacturing process involving the
use of hot melt resins. It is a cost effective
alternative to epoxy potting for protection
of fragile electronic components.
Jim Marshall is with the adhesive technology
division of Henkel, maker of
Macromelt and Loctite products
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Within the automotive industry, for
example, the technique can be applied to
various electronic systems and devices,
such as tyre pressure monitoring systems
(TPMS), PCBs for seat occupant sensors,
belt lock sensors, ECUs for motorcycles,
air quality sensors, antennas for RF
devices, and smart entry systems.
Although the automotive industry has
been the significant beneficiary of this
technology, there are numerous other
applications within a vast array of industry
sectors. Such applications include the
protection of light barriers, connectors
and grommets in the heavy environment
of machines tools. Not only does the
technique offer a high quality end product,
but also assembly times are considerable
reduced. The traditional method
involves making a mould case, palletising,
inserting the electronics, pre-heating
the assembly, encapsulating, setting or
vacuuming, curing and then testing.
Using hotmelt resins, there are just
three steps – inserting the electronics into
the enclosure and over-moulding, followed
by testing.
Applications
There are three main application groups
where this moulding practice comes into
its own. The first involves electronic
component encapsulation. Here, the low
pressure applied during the moulding
process prevents damage to the sensitive
electronic components and elements.
Indeed, the moulding protects the electronics
from external influences, such as
moisture and mechanical stressing, and is
capable of serving as a housing.
The second area includes connector
potting. In these applications the hotmelts
are used for sealing the plug and
also for cable strain relief.
Finally, the process can be used to
mould grommets in place. This eliminates
the time-consuming process of slipping
on the grommet, which can cause
repetitive strain injury. The moulding
can also include strain relief, which also
enhances its aesthetics.
Renewables
The hotmelts used for this technology are
polyamides based on dimer fatty acids.
These fatty acids are obtained from
renewable resources such as soy, rapeseed
and sunflowers and then dimerised.
Because they are harder and tougher
than other hotmelt systems, products
such as the Macromelt range have characteristics
similar to those of plastics. In
moulding technology, these resin systems
do indeed perform the functions of plastics.
Put simply, the resin does not form
a thin film between two substrates, but
actually become integral to the external
3-dimensional form.
In reality, this means housings of thermoplastics
can be fully replaced by these
resin systems. At the melt temperature
these hotmelts actually form a resin bond