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Tab
Positioning
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Necessity of providing Tabs
for the component: |
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To prevent components becoming
detached from the main sheet and being lost in the etching
machine sump.
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To prevent
complex components getting entangled while stripping off the
photo resist
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Tabs are often
drawn across the etch Bands. These are in triangular shape &
apex pointing towards the components. After etching, the
Apex size would be equal to thickness, so that the
components can easily be broken out from the retaining
sheet. Figure 1 shows both Internal & external tabs (only
for illustration,) Our process can provide either of the two
Internal or External Tabs.
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Dimensions
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For
dimensions of slots, hole opening and metal corners there are
a few guideline’s for designers, which express practical
limitations. The most common rules are as follows: |
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Relationship of hole diameter
to metal thickness : |
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The diameter of hole
achievable by our process is minimum 1.5 times of the
thickness or more.rner Radius to Metal Thickness.
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The Internal radius of smallest
corners in the component which can be achieved by our
process is equal to the thickness of the metal i.e. for
metal thickness of 0.05mm, corner radius would be 0.05mm
min.
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Relationship
of Inside Corner Radius to Metal Thickness |
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The smallest
corner of radius is approximately equal to the thickness of
the metal i.e. for metal thickness of 0.05mm, corner radius
would be 0.05mm |
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Relationship
of Outside Corner Radius to Metal Thickness |
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Outside corners tend to etch
more sharply than inside. Therefore a radius of less than
metal thickness is achievable. As a general rule outside
radius is considered to be at least 75% of the metal thickness
T. |
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Relationship
of Line Width to Metal Thickness |
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The width of
metal between the holes is not a problem in photochemical
etching but when this space is the remaining surface area in a
large field of slots/holes then there are limitations as to
how small the metal width between the holes can be . |
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Relationship
of Bevel to Metal Thickness |
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An etchant attacks the material
laterally as well as vertically Assuming that the material is
being etched equally from two sides, it can be easily seen
that a bevel is produced. As a general rule, when etching from
two sides, the bevel is Approximately 10% of metal thickness
as shown in figure. |
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Etched
Dimensions
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Because of
the many parameters involved in determining etching
Tolerances, it is not practical to give a definite rule, which
will cover all circumstances. Some of the more common
variables, which will affect the etching tolerances, are type
and thickness of metal, size of production run and number of
critical dimensions per piece. For purpose of establishing
some general rule of thumb, a tolerance chart of metal
thickness indicating the etched dimensions that are achievable
for the said raw material thickness is mentioned below: - |
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THICKNESS
(MM) →
MATERIAL ↓ |
0.05 |
0.15 |
0.25 |
0.50 |
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DIMENSIONAL TOLERANCE
ACHIEVABLE (MM) |
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Aluminum
alloys |
±0.02 |
±0.03 |
±0.04 |
±0.08 |
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Copper &
it's Alloys |
±0.01 |
±0.015 |
±0.025 |
±0.05 |
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Nickel |
±0.01 |
±0.015 |
±0.025 |
±0.05 |
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Steel
Alloys |
±0.01 |
±0.015 |
±0.025 |
±0.05 |
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Stainless
Steel |
±0.01 |
±0.023 |
±0.038 |
±0.075 |
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