What Causes PCB Warpage & How To Avoid It - Miracle Electronics

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What Causes PCB Warpage How To Avoid It? -
Miracle Electronics Imagine, you receive a PCB
package, but when you place it onto your
application device, you realize that it doesnt
fit into the flat space available! Can you
envisage how annoying and bothersome that may
be! The reason behind such a scenario is board
warping, the unintended change in the geometry
of a PCB. A warped PCB is thus an altered PCB,
regardless of the shape it forms into, such as
bow, twist, etc. In short, a warped PCB is one
that does not sit accurately on a flat surface.
What causes PCB warpage? There are several
reasons that could cause PCB warpage, but there
are two specific causes one of them could be
layout- related, while the other could be
process-related. If the PCB is warped before the
beginning of the assembly process, the problem
lies between the layout and fabrication. But, if
the PCB was flat earlier, and warped after
assembly, then the problem lies between the
fabrication and assembly.
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Design issues causing the warpage There could
be certain design issues that may contribute to
PCB warpage, which need to be first and foremost
eliminated, before moving onto the fabrication
or assembly process. And, in order to eliminate
them, you first need to know the main design
contributors some of them being odd shapes,
large cut-outs, a thin board, grouping together
of heavy components, and uneven copper
pour. Assembly issues causing the warpage If
polyimide or FR-4 is used to build a PCB, and a
stack of such bare boards are stored for some
time before assembling, they may absorb moisture
from the environment, to eliminate which it is
customary to bake them for at least 3 hours at
80-150C first, and then cool them to room
temperature before assembling. Another reason
for warpage in large boards may be related to
the orientation as the boards enter the reflow
oven. In order to prevent uneven heating between
the edge of the PCB and the middle, the larger
dimension must be placed parallel to the
conveyor of the oven. Small PCBs are generally
grouped together to form panels for more
efficient assembling, after which they are
separated manually into individual PCBs. The
separation takes place by either breaking them
away or through V-scoring. In the process of
breaking away, most of the material between the
smaller PCBs is cut away, leaving them joined by
only small lands and if the panelization is
large, the cut-outs could lead to warping. On
the other hand, V-scoring is where a V- shaped
groove forms the separation line, instead of
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removing a part of the PCB, which prevents
warping of the panel during assembly, while
making it easier to separate the boards. How to
prevent PCB warpage? ? Storing the PCBs properly
before the assembly process is crucial in
preventing warpage. Standing them on their edge
cannot guarantee that they will be vertical all
the while. Moreover, the combined weight of the
PCBs will ultimately cause a camber. It is thus
important that the PCBs are stored properly, and
horizontally on a flat surface. ? PCBs should
be stored in an area where the temperature and
humidity is under control, because it is usual
for PCBs to absorb moisture from the
surroundings. And, where it is impractical to
control the environment, desiccants can be used
to control the moisture. ? Just like PCB
fabricators use heat to form multi-layered
boards (https//www.miracle.net.in/blog/building-
effective-multi-layer-printed-circuit-board/), re
- application of heat to warped bare boards can
help straighten them as well. But, this may
require heavy- pressing the boards between
heated smooth steel plates for 3-6 hours and
baking the PCBs 2-3 times. In order to prevent
such warpage in your PCBs, you need to ensure
that you get your PCB assembly from India from
an experienced manufacture, who knows how to take
care of every process involved in storing and
manufacturing the
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PCBs well, such that every PCB is built
successfully and effectively.
For more Information https//www.miracle.net.in/