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Mean
time between failure:
(see MTBF)
Melting Range:
The difference between the solidus and liquidus temperature.
Mesh Porosity:
The ratio of the amount of open area in a mesh versus the
amount of closed area in a mesh.
Mesh Size:
The number of openings per inch in a screen. For example,
a 325 mesh screen has 325 openings per inch.
Metal Composition:
The composition of metals in an alloy that go into solder
paste.
Metal Content:
The percentage weight of the solder alloy powder in solder
paste.
Metal-Core Boards:
Boards built with a metallic core and an organic or inorganic
insulation on either sides of the core. The core could be
made of steel, stainless steel, aluminum, copper, or a laminate
of metals (in most cases copper invar copper or copper tungsten
copper). The insulation of the core is done prior to metallization.
Metering Rolls
: Successive rollers used to control the fabric to
resin ratio during the impregnation of resin onto glass fabric.
Micron:
One millionth of a meter, and another term for micrometer.
An easy conversion scheme is to remember that 25.4 microns=0.0254mm=0.001"=1
mil=1,000 microinches. With this formula memorized, it is
simple to translate between inch and metric references.
Microstructure of Material:
Atomic structure of a material. In bonding applications, refers
to the effect of atomic structure on material behavior during
various steps in the excise, form, and bonding processes.
Misalignment:
Misregistration of the centerline of the component lead with
respect to the centerline of the bonding pad on the substrate.
Misregistration:
The lack of adequate dimensional conformity between two or
more patterns or features. Examples include misregistration
of a board with respect to a stencil or the misaligment between
layers of a printed circuit board.
Mold Flash:
Plastic debris remaining on a plastic molded package after
the component manufacturing process. This can occur on molded
carrier ring (MCR) and plastic quad pack (PQFP) components.
Molded Carrier Ring (MCR) Component:
A packaging technique for ICs that utilizes a plastic molded
body and guard ring. MCR were developed to reduce damage to
leaded surface mount packages caused by normal handling. The
guard ring also acts as a common form factor for the development
of automation such as test, burn in, and excise and form.
MTBF:
The statistical mean average time interval, usually in hours,
that may be expected between failures of an operating unit.
Results should be designated actual, predicted or calculated.
Multichip Module:
A module capable of supporting several ICs in a single package.
Typically, multichip modules are based on ceramic, contain
high performance ICs with high pin count, and use some form
of advanced interconnect technology such as TAB, COB,
or C-4. The parameters used to define a multichip module are
vague, but one basic criterion is a package that is no less
that 20% silicon, has no fewer that 100 I/O on a substrate,
and has no fewer that four layers.
Multilayer Board:
A PCB that uses more than two layers for conductor routing.
Plated via holes are used to connect the internal layers to
the outer layers.
Multilayer Ceramic:
A stack of alternating metallic and ceramic layers with vias
interconnecting them.
Multilayer Substrate:
Organic substrates composed of more than one laminate. Cofired
multilayer ceramic substrates are also referred to as multilayer
substrates.
Multiple Metal Layer Tape:
An advanced TAB tape that has more than one conductive layer.
This tape design is complex, including ground planes and interconnections
between conductive layers, and is only used in select high
performance applications.
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