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TYPICAL CUSTOMER QUESTIONS
What is the Ohmega-Ply® resistive material made of?
Ohmega-Ply® is a true thin-film, Nickel-Phosphorous (NiP) alloy. In
the manufacturing process, about 0.1 to 0.4 microns of the alloy is electro-deposited
onto the rough, or tooth side, of electrodeposited copper foil.
What types of copper is it available on?
The copper foil is standard electrodeposited copper. Both single and double
treat coppers of 0.5 oz, 1 oz and 2 oz weights are available.
What types of dielectric are available?
The Ohmega-Ply® product is sold either in an unlaminated form (Ohmega-Ply®
RCM, or Resistor-Conductor Material), or laminate form. Ohmega Technologies
subcontracts the lamination to the independent laminators. Ohmega-Ply®
is therefore available on most dielectric materials now offered in the industry.
What is Ohms per Square?
Ohms per square is a dimensionless square area of resistive material, the
length and width of the resistor being of equal size, having an Ohmic value
equal to the sheet resistivity of the resistive material deposited onto
the copper surface. A 25 ohm sheet resistivity material would yield a 25
ohm resistor whether 1 mil wide by 1 mil long, or 1 inch wide by 1 inch
long.
What resistive values are available?
Ohmega-Ply® is available in 25 ohm per square, 50 ohm per square and
100 ohm per square sheet resistivities at + or - 5% tolerance. A 250 ohm
per square product is available at + or - 10% tolerance.
What size does the Ohmega-Ply® material come in?
The various sheet resistivities are manufactured reel to reel on equipment
using two standard copper widths: 40" and 45". The lengths can
vary, but the sheeted product is usually 51" long to accommodate the
laminators press size requirements. The RCM can be cut to custom sizes,
if required.
What resistor values can be designed using Ohmega-Ply®?
The resistor values are a function of the available board area for routing
the resistors, the resistor size, and the sheet resistivity used. The 25
ohm per square product is used to create resistors with an approximate range
of 10 ohms to about 500 ohms. The 50 ohm per square product is used for
resistors with an approximate range of 25 ohms to about 10,000 ohms. The
100 ohm per square product is used for resistors with an approximate range
of 50 ohms to about 25,000 ohms. The 250 ohm per square sheet resistivity
is normally used for higher values in the 500 ohm to 1 Megohm (1 million
ohm) range. This is a general rule. Resistors of higher and lower values
with each of the sheet resistivities can, and have been, designed into circuit
boards.
Can I have multiple values of resistors on a layer?
Yes. The value of the resistor is determined by the ratio of the length
of the resistor to it's width multiplied by the sheet resistivity used.
The number, and values, of the resistors used are a function of the dimensions
as defined in the artwork.
Must you add a layer to a circuit board to use the Ohmega-Ply® resistors?
No. The resistors are almost always incorporated into an existing plane
of circuitry. For parallel termination and pull-up applications, the resistors
are usually placed on a voltage plane. For series termination the resistors
are usually placed on a signal plane. The resistors can be used on an internal
layer of the circuit board, or can be used on a surface layer.
Can I use more than 1 layer of the resistive material in the circuit
board?
Yes. There are numerous applications which now use more than one layer.
There is no maximum number of layers that can be used within a circuit board.
What is the tolerance of the final resistors?
The nominal cumulative resistor tolerance is a function of resistor size,
number of resistors on the board and the size of the board itself. Normally,
a 10% - 15% tolerance is achievable for resistors which are multiple squares
and a minimum of 20 mils wide. Boards which are large, or have a large number
of resistors, some provision for a few resistors to be out of the 10% tolerance
range would be desirable. Most applications for termination or pull-up resistors
can accommodate this tolerance range. For partial square resistors or designs
using 100 ohm per square material with multiple resistor values and shapes
on a layer, a 15-20% tolerance is what most board shops request. For analog
applications where a tighter resistor tolerance (1-2%) is required, resistor
trimming has been done in Japan. Ohmega-Ply® trimming in the U.S. is
now just emerging. (Please go to New to the Site
to get more information about Ohmega Resistor tolerance)
What is the minimum size the resistor can be made?
The size of the resistor is only limited by the board shop's ability to
etch accurate lines. However, as a rule of thumb, the larger the resistor,
the better. Most resistor line widths are between 10 and 20 mils, with 20
mils being the most common. There are some resistors which have been designed
with line widths less than 10 mils, but currently these are the exception
rather than the rule.
What kind of power rating do the resistors have?
The amount of power that can be applied to the resistor is limited by the
size of the resistor, the thermal management of the heat generated from
the resistor, and the type of dielectric material used. A typical power
rating would be about 1/8 watt, but this can be increased with the use of
heat sinks and higher temperature laminate materials.
When does it become cost effective to use Ohmega-Ply®?
The use of Ohmega-Ply® provides both design and cost benefits. A number
of cost savings are realized by eliminating discrete resistors, including
the cost of the discretes and their accompanying direct and overhead costs
of inventory, assembly and rework. These costs will vary from customer to
customer. The greater the resistor density, the greater the cost savings.
For a pure "retrofit" design which replaces discrete resistors
with Ohmega-Ply® and with no design enhancements or improvements, the
cost benefits usually begin if the resistor density is approximately 3 to
4 resistors per square inch of board. For applications where there are design
enhancements and/or board improvements (e.g. double sided SMT being designed
into a single sided SMT board), the cost benefits can begin at a lower resistor
density.
How much more does a finished circuit board cost with Ohmega-Ply®?
For a typical board size of 18" x 24" (3 square feet) a board
shop would add about $200 for low volume applications and about $90 to $100
for high volume applications to the price of the board. This adds between
$0.21 to $0.46 per square inch to the finished board depending on the board
volume and the technical difficulty associated with the board manufacture.
The added cost would be offset by the elimination of the discrete resistor
costs and the costs of assembly, rework and inventory as well as the design
and electrical enhancements to the finished circuit board.
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