All dimensions, tolerances
and configurations are functions of the thickness of the material being photo
etched and should be considered during the design process. The following guide
gives practical limitations for slots, spaces, holes and construction
dimensions with relation to metal thickness for photo chemical milling. (See
Figures 1 and 2 for a representation of the features referenced.)
In many cases it may be possible to exceed these photo etching limitations, but
with a reduction in yield percentage. Consult the factory for design assistance
when these situations occur.
DIMENSIONS
HOLES
/ SLOTS
Generally, the diameter of
a hole or the width of a slot cannot be less than the metal thickness. This
relationship varies as the metal thickness changes. A more exact relationship
is illustrated in Table 1.
Table 1. HOLES OR SLOTS
Metal Thickness (T)
Diameter or Width
.001"-.005"
At Least Metal Thickness, Min. .003"
.005" or Over
Min. of 1.1 Times Metal Thickness
INSIDE
CORNER RADIUS
The smallest inside corner
radius is directly proportional to the metal thickness. *Consult our sales staff if
a smaller or sharp radius is required.
FINGERS
/ WEBS
Generally, the width of a
finger or web cannot be less than the metal thickness. This relationship varies
as the metal thickness changes. A more exact relationship is illustrated in
Table 2.
Table 2. WEB OR FINGER
Thickness
(T)
Spaces Between Holes (W)
Less than
.005"
At Least Metal Thickness, Min. .003"
Over
.005"
Min. of 1.25 Times Metal Thickness
OUTSIDE
CORNER RADIUS
The outside corner radius
will be at least .75 of the material thickness.
TOLERANCES
CENTER
TO CENTER
Generally, the tolerances
are a result of the stability of the photo tooling material. Table 3
illustrates the practical tolerances attainable from industry standard Mylar
tooling. Consult our sales staff for information on alternate tooling materials.
Table 3. CENTER TO CENTER TOLERANCES
C/C
Dimensions (inches)
Tolerance Attainable
1.0" or
Less
±.0005"
1.0" -
6.0"
±.0010"
6.0" -
12.0"
±.0015"
12.0" -
24.0"
±.0020"
PHOTO
ETCHED DIMENSIONS
Generally, a tolerance of ± 15% of the material thickness is
practical. A more exact relationship is illustrated in Table 4.
