BioSciences - Polysciences, Inc.

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Electronic Adhesives & Encapsulants
Modulus is frequently shown as a stress-strain graph:
Stress
Strain
In semiconductors, modulus is an indication of a material’s ability
to absorb stress induced during curing and temp cycle due to
CTE mismatches between the die and substrate. The lower the
elastic modulus the more stress absorbing capability. The unit of
measurement for modulus is usually Giga-Pascal (GPa).
MSDS: Material Safety Data Sheet. Document that provides
end users with chemical composition and safety information.
It also includes handling information that is required by OHSA
(Occupational Health & Safety Administration) in the US.
MONOMER: A molecule that can combine with others to form a
polymer. During the curing process, monomers are joined together
to form polymers.
OUTGAS: Amount of weight loss of an adhesive during curing or
at elevated temperatures. Any solvent and low boiling temperature
components of the polymer formulation can evaporate. The
temperature and conditions entirely depend on the materials of
the formulation. Bubbles formed as the outgas material tries to
escape can form voids in the die attach, underfill or encapsulant.
These voids can interfere with conductivity and adhesion. The gas
can also condense on nearby bond pads and leads interfering with
wire bonding.
PCT (PRESSURE COOKER TEST): Way to accelerate testing the
moisture and temperature resistance of a device. Parts are put in a
chamber at 2 atmospheres with water at 121°C to determine their
moisture resistance. Since an autoclave is typically used for this
test, it is also called the Unbiased Autoclave Test (JEDEC A102).
The HAST (Highly Accelerate Stress Test) is a higher pressure and
temperature version of the PCT in reliability testing.
pH: A measure of the acid/base nature of a material. Neutral,
neither acid nor base, is a pH of 7. Numbers below 7 are very
acidic. Numbers higher than 7 are very basic. The further the pH
is away from 7, the stronger the acid or base. High pH materials
can be present in detergents and soaps. Fluxes can be acidic.
Extractable ionic contaminants in the epoxy materials can alter the
pH from neutral in the presence of moisture. The acid or base
formed by the ionics can causing corrosion.
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POLYMER: Compounds consisting of large molecules made up
by a linked series of short molecules called monomers. When
the short molecules join together to form the long molecules,
the material is said to have cured or polymerized. The structure
of the polymer contributes most of the physical characteristics of
materials containing them.
POLYMERIZE: Bonding of two or more monomers to form a
polymer. The process of polymerizing is also called curing.
POT LIFE: Also known as working life. This is an indication of how
long the material can be held at room temperature and still be
processed. Two factors contribute to pot life limitations:
1) Increases in viscosity because the material begins to polymerize
at room temperature; and 2) settling or separation of filler from
the resin. In both cases, inconsistent dispensing results and
performance in the finished package is inconsistent.
POTTING COMPOUND: Resin used to encapsulate or seal large
areas of a device or combination of devices. Potting compounds
are normally poured or dispensed into a device enclosure, filling
the entire area.
REFLOW TEMPERATURE: Temperature that the device is sent
through to melt solder. For lead solders this is typically 230°C, for
lead free alloys the value is 260°C.
RESIN: Term used for the liquid portion of epoxy formulations.
The resin is the polymer that performs the chain branching
and crosslinking during cure. Resin provides many of the key
performance properties of the resulting cured polymer. Unfilled
materials are 100% resins. Filled materials such as die attach
adhesive and underfill contain 20% to 40% resin.
RHEOLOGY: Description of the flow characteristics of a fluid. The
properties of viscosity and thixotropic index are descriptors of the
rheology of a material.
SEPARATION: Also known as Filler Settling. In Silver or Silica
filled materials, the particles are in suspension from the mixing
process. These products are frozen to the fillers in suspension and
uniformly dispersed throughout the resin. At room temperature,
gravity will cause the more dense filler particles to settle through
the lighter polymer.