Rigid Flex PCB Design: Benefits and Design Best Practices

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A Must Read PCB Material Guide

• A MUST READ PCB MATERIAL GUIDE    
• Before we talk about PCB material, lets started
  with a PCB introduction.PCB is a self-contained
  component of interconnected units found in
  gadgets ranging from ordinary beepers or pagers
  to complex radar and computer programs. A thin
  layer conducting substance printed or deposited
  on the insulating board called the substrate is
  used to develop circuits. The specific electronic
  units are put on the substrates surface, which
  is then soldered to the interlocked circuits. It
  is common to have PCB performing one role, for
  instance, a signal amplifier or a number of
  functions. There are main types of PCB
  construction. These include
• Single-sided PCB
• Double-Sided
• Multi-layered

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A MUST READ PCB MATERIAL GUIDE   
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PCB is the most critical part component of
electronics. You may have heard of the printed
writing cards or printed writing board when
individuals talk about PCB. Well, there is no
difference between these terms they mean the
same thing. Due to their significance in all
electronics, including computers and calculators,
the board material for the PC is chosen with a
lot of care and caution. The person making the
selection must have knowledge of the electrical
requirements of any type of equipment.
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A MUST READ PCB
MATERIAL GUIDE   
Prior to the establishment of PCB, the materials
used for early boards were often covered by
shells of knotted overlapping wirers, which could
fail at particular junctures. When used for
relatively long, they could as well short
circuit, and some wires could start cracking.
Expectedly, the manual process used in making
these boards was so demanding, confusing, and
meticulous. Since many electronics started
depending on circuit boards, it became
increasingly necessary to come up with modest,
more compact options, and this is precisely what
led to the emergence of PCB material.
Importantly, the metal, which enhances the flow
of current between the board and the components
attached, is referred to as solder. This
substance has dual roles considering its adhesive
features. This blog covers all the details you
need to know about PCB materials. So read to the
end, and you will enrich your knowledge and
perhaps make the right choice when required.
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The Basic Properties
of PCB Material
This is perhaps the most crucial aspect you need
to pay attention to. As we mentioned at the
outset, you need to be careful while selecting
the PCB material, and being acquainted with the
properties is so crucial. In this section, we are
going to look at thermal, electrical, and
chemical properties. So let us begin Thermal
Properties As the title suggests here, we
examiner the effect of temperature. Pay attention
to the following. The Glass Transition
temperature. Temperature ranges affect PCB
material significantly. Generally, the substrate
softens if subjected to a temperature beyond the
required threshold. But again, the substrate will
harden when taken back or when the temperature is
readjusted to normal. The range where
transformation can possibly occur is called glass
transition temperature (Tg). This unit is
determined in degrees celsius.
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The Basic Properties
of PCB Material
The Decomposition temperature. This is a
temperature within which decomposition of the PCB
material takes place. Generally, when the
substrate is in temperature beyond a particular
threshold, it decomposes. Unlike in glass
transformation, the effects of substrate
decomposition are irreversible. Why does this
imply? People work in different environments with
different temperature ranges. When selecting a
PCB substrate, you need to ensure it is really
compatible with your working environment.
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The Basic Properties
of PCB Material
Coefficient of Thermal Expansion. The expansion
rate of any PCB substrate is the CTE. Whenever a
material his subjected to a temperature beyond
its Tg, the CTE rises, and this is quantified in
parts per million (ppm). A PCB material often has
a greater CTE compared to a copper layer. In most
cases, this deviation in temperature is the
leading problem of interconnection issues when
heated. However, because of the constraints in
the PCB material as a result of the glass woven,
CTE is generally within 10 to 20 ppm in the X and
Y axes. In case the temperature goes beyond the
Tg limit, the CTE does not change.
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The Basic Properties
of PCB Material
Thermal conductivity. The heat conductive
characteristics of PCB material is called thermal
conductivity (k). The thermal conductivity of a
substance is directly related to the potential of
a PCB material to transfer heat. The thermal
conductivity is determined in in watts per meter
(w/m), expressed in kelvin (k) In light of the
above, the thermal properties of a PCB substrate
is a vital factor for consideration. PCB
materials are significantly affected by
temperature ranges, and so you should pay
attention to the conditions in your working
environment. What about the electrical properties?
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The Basic Properties
of PCB Material
Electrical Properties of PCB material There are
several electrical characteristics you need to
consider when it comes to the choice of a PCB
material. The following is a brief overview of
some of them. Dielectric constant. This feature
is Relative Permittivity. Impedance and integrity
are the two most significant factors for
consideration when it comes to the electrical
performance of a PCB substrate. The dielectric
constant of a PCB material range from 3.3 to 5.5.
This value is affected by frequency.
Specifically, it is inversely related to the
frequencies. Nevertheless, Er changes differently
in different materials. It changes less in others
and more in others. For a substrate to be safer
for use in high-frequency applications, it should
have a stable dielectric constant in wide
frequency ranges.
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The Basic Properties
of PCB Material
Dielectric Loss Tangent (Tan d). It is also the
Dissipation Factor (Df). If a material has a low
loss tangent, it actually loses less power. The
loss tangent applied in the PCB materials often
varies from 0.02 to o.oo1. The higher value
applies to most of the materials, while the
latter one is used in the high-end materials.
Besides, the loss tangent is also affected by the
frequencies. It increases with a rise in
frequencies. However, on the basis of digital
circuitry, the loss tangent is not very
significant.
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The Basic Properties
of PCB Material
Volume Resistivity (?). This is the resistance of
any dielectric substance to insulation or perhaps
electricity. If a PCB substrate has a great
resistivity, it is not likely to expedite
electric charges. The resistivity of any
dielectric substance is measured in
ohm-meters (O-m) or ohm-centimeters (O-cm). Just
like in the dielectric insulators, all the
materials on the PCB needs to have high
resistivity. The preferred resistivity value
range between 103 and 1010 Megaohm-centimeters.
Nevertheless, external factors such as
significant temperature variations and humidity
influence the resistivity of a substance. Surface
Resistivity (?S). This is the surface resistance
of a dielectric substance to insulation as well
as electricity. Just like the volume resistivity
of a material, surface resistivity needs to be
high. It should range between 103 and
109 megaohms per square. Also, differences in
temperature and moisture influence surface
resistivity.
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The Basic Properties
of PCB Material
Electrical Strength. Throughout the Z direction
of a PCB substrate, the potential of a dielectric
substance to withstand electrical breakthrough is
called electrical strength. This is determined in
volts/mil. Most PCB substrates electrical
strength falls between 800 V/mil and 1500
V/mil. Indisputably, the electrical
characteristics of a PCB material is a vital
factor for consideration. From the above
discussion, it is crucial to pay attention to
these properties when making your choices. Let us
now look at other aspects of PCB material
properties.
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The Basic Properties
of PCB Material
Chemical Properties The following are the
critical properties for consideration in this
regard. Flammability Specs (UL94) Moisture
Absorption. This is the capacity of a dielectric
substance to resist exposure to a liquid. The
moisture absorption figure for many PCB materials
ranges from 0.01 to 0.2. In general, moisture
absorption affects both the electrical and
thermal characteristics of dielectrics. Methylene
Chloride Resistance (MCR). This is the chemical
resistance of any PCB substance. This measures
the dielectric strength of methylene chloride
absorption. The MCR often ranges from 0.01 to
0.20.
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The Basic Properties
of PCB Material
Types of PCBs As we stated at the outset, there
are three main variants of PCB materials. Let us
now review them in detail. Single-layer PCBs As
the name suggests, this is a PCB made from one
layer of the base substance. Usually,  a tinny
metal layer covers one side of the base
substrate. Since copper is the most fantastic
electrical conductor, it is always preferred as a
coating. Upon applying the copper base platting,
a protective solder mask is often applied.
Finally, the last silk-screen is used to mark out
all the essential units on the board. Single-layer
PCBs are quite easy to create and manufacture.
This is due to the fact that they have different
circuits and units soldered on a single side. For
this reason, single layer PCBs can be acquired at
relatively lower prices, especially where one
makes a large volume purchase. They are used for
different applications such as calculators,
printers, and power supplies, among others.
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The Basic Properties
of PCB Material
Double layer PBCs Unlike single-layer PBCs,
double layer PBCs are characterized by base
material having a slim layer of a conductor, such
as copper on both sides. Holes are often drilled
on the board to enable circuits on one section of
the board to link to the circuits on the end. In
the double layer PCB board, the circuit and the
components are often linked in two ways. The
first one can be using a through-hole and a
second one utilizing a surface-mount. In general,
a through-hole connection simply means the minor
wires, also referred to as leads are always fed
via the holes. Afterward, the leads are soldered
to the appropriate component.
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The Basic Properties
of PCB Material
In contrast, the wires are not used in the
surface mount as connectors. In this case, a lot
of soldered small leads are directly linked to
the board. This implies that the board itself is
a wiring surface for various components. This
permits the completion of the circuit with
limited space. A lot of space is freed, and as a
result, the board can carry out more functions at
a faster speed and a lightweight compared to when
through-board holes are used. Usually, double
layer PCBs are utilized in the applications
demanding an intermediate degree of circuit
complexity, including the following Industrial
controls Power supplies Instrumentations LED
lighting Automotive dashboards Amplifiers Vending
machines
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The Basic Properties
of PCB Material
Multilayer PCBs Multilayer PBC is made up of a
series of either triple or a number of
double-layered PBCs. A specialized glue is often
used to secure these layers before they are
sandwiched between insulation units to make sure
too much heat cannot melt or soften any of the
individual components. Additionally, these PBCs
are always in a variety of sizes. They can
contain only four layers, or as many as ten or
twelve. The biggest multilayer PBC ever to be
designed was 50 layers in thickness. If a PBC has
a lot of layers, developers can come up with
quite thick, complex structure appropriate for a
wide range of intricate electrical functions.
Multi-layer PBCs can be pivotal in the following
applications
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The Common types of
PCB Materials
There are three common materials crucial in the
fabrication of the PBCs. The following is a brief
overview of each of the three. FR-4        This
is the widely used material in the manufacture of
PBCs. It is just a glass strengthened epoxy
laminate sheet. The laminate that is utilized
here flame retardant and also resistant to water.
It also offers better strength when it comes to
weight ratios. The material provides a very high
tensile strength. PTFE (Teflon) This is basically
a plastic substance with no resistance. For this
reason, it is utilized for fast speed and
frequency applications. This material has a lot
of advantages. For instance, it is very flexible,
making it priceless in applications having tight
tolerances. Additionally, it is very lightweight,
making it usable across different industries.
Moreover, it is flame resistant, has great
physical strength, temperature stability, and
quite versatile in application.
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The Common types of
PCB Materials
Metal This is a conventional material of copper
and aluminum, among others utilized in PCBs. They
permit the usage of Surface Mount Technology for
the incorporation of components. They also have
mechanical durability and, therefore, can be used
for long.
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The Common types of
PCB Materials
The Future of PCB Material The shrinking of the
electronic devices will lead to the production of
smaller and densely packed PCBs. These products
will have significant electric potential. The
development beyond the boards we just discussed
here comprises of 3-dimensional molded plastic
boards as well as the increased utilization of
the integrated circuit chips. For this reason,
the manufacture of PCBs is likely to be more
dynamic in the years to come.
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The Bottom Line PCB materials have a lot of
characteristics. It is essential to consider all
these characteristics are essential, and you have
to consider them when selecting the materials for
use in this regard. Some characteristics, such as
decomposition temperature and glass transition
temperature, are significantly affected by
temperature variations. For this reason, you are
supposed to consider the temperature of your
working environment when selecting PCB materials.
If you need help in choosing PCB material, try
seeking help from Moko Technology.
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