BioSciences - Polysciences, Inc.

SHEAR STRENGTH: Key measure of adhesion for die attach
adhesives and underfills. A shear strength tester pushes a die or a
test part with increasing sideways force until the bond fails. Shear
strength is reported in Kilograms (Kg), Kilograms Force (Kg-f), Kg/
cm^2, and PSI. The total force is a function of the die size and
type of substrate so it is important to always describe the parts
being tested. Dage and Royce are two main suppliers of shear test
equipment.
SHELF LIFE: Length of time that a material may be stored and still
perform per specification. Many polymers require storage at low
temperature in order to be stored successfully. This temperature is
typically -40°C for most polymers used as adhesive and +4°C for
molding compound. Two things lead to limits in shelf life; curing
of the polymer and separation (settling) of the filler.
SILICA: Common name for Silicon Dioxide. Silica is the most
commonly found material on earth. Silica has a very low CTE
(as low as 1.5ppm), is chemically inert and in some forms can
be inexpensive. It is an ideal material to use as filler for polymer
materials. Silica comes in two common shapes, angular and
spherical. The angular Silica is a ground up natural material (sand)
and is very inexpensive. It is widely used for low cost applications
such as low end molding compound. Unfortunately, because
it has sharp points, it does not flow easily around obstructions
(like solder bumps on a Flip Chip). It is also very abrasive and can
scratch the very thin oxide on the surface of a die. Spherical Silica
is fused (melted) to remove the sharp points and is preferred for
advanced applications. Because the material is made using more
steps it is more costly. As applications require the polymer to flow
into very tight spaces (e.g., between fine pitch wires or low Flip
Chip bumps) the Silica particles must be very small, typically not
larger than 1/3 the narrowest gap.
SILICONES: Organic compounds containing Carbon, Hydrogen,
Silicon and Oxygen. Because they contain Silicon and Oxygen
they are also part of the larger set of chemicals called Siloxanes.
Silicones are generally stable chemicals that resist many chemicals,
have good adhesion when formulated as adhesives, resist moisture
and are very flexible.
SILVER: Most commonly used conductive filler material. Silver
is relatively inexpensive (compared to Gold), and is an excellent
electrical and thermal conductor. Commonly used as flakes (tiny
sheets) or kernels (rough spheres).
SINGLE COMPONENT (1K): Polymer that is premixed and ready
to use, requiring shipping and storage conditions below -40°C
to inhibit cure. 1K is also referred to as 1 part. Some polymers
require mixing two or more separate liquids just before customer
use. These are dual or multi component materials commonly called
2K or 2 part.
Electronic Adhesives & Encapsulants
SLUMP: When screen printing or dispensing a relatively thick (tall)
quantity of material, the material can collapse along its edge. This
collapsing is known as slump. Slump limits the practical height
to which a material can be screened or dispensed. As a rule of
thumb, materials cannot be printed with a height that is more
than 50% of the width of the finished pattern. This is known as
the Aspect Ratio. If the height is the width of a dam, the Aspect
Ratio is 1 to 2.
SNAP CURE: Describes die attach materials that cure in less than
two minutes.
SOLVENT: Material used to dissolve a solid or to reduce the
viscosity of a liquid. Many commonly used semiconductor polymers
are so highly viscous that they require the addition of a solvent in
order to get satisfactory flow. This solvent typically must evaporate
(boil off) during the curing process. If not properly managed, this
can lead to voids in the cured material.
SYNTHESIS: Formation of a compound from simpler compounds
or elements. When organic chemicals are combined to create new
properties without changing the structure of the molecules they
are said to have been formulated.
Tg (Glass Transition Temperature): Most materials such
as metals and ceramics do not have any sudden shift in their
properties over temperature. The properties may change slowly,
but the change is continuous. That is not true for most polymers.
Many polymer materials undergo an abrupt change in their
mechanical properties at a temperature which is called the glass
transition temperature. Below the glass transition temperature,
polymer materials are somewhat glass like, they are stiffer and
have relatively low CTE. Above the glass transition temperature,
polymers are less stiff but have higher CTE. In some polymers the
change in properties can be very large. For example the CTE above
the Tg can be three times than below it. This makes Tg and CTE
a very important contributor to stresses generated by thermal
changes.
THERMAL CYCLING: General term that refers to repeatedly
raising and lowering the temperature of a circuit to see if it
deteriorates. Cycling can be done by moving the test unit between
temperature extremes slowly or rapidly. If cycling is done rapidly it
is referred to 1,000,000 cps.
For more information please call (800) 523-2575 or visit: www.polysciences.com 327