Definition of OhmegaPly®
OhmegaPly® is a thin film Electrodeposited‐On‐Copper NiP metal alloy (RESISTOR‐
CONDUCTOR MATERIAL) that is laminated to a dielectric material and subtractively
processed to produce planar resistors. Because of its thin film nature, it can be buried within layers without increasing the thickness of the board or occupying any surface space like
layers without increasing the thickness of the board or occupying any surface space like discrete resistors.
COPPER
COPPER
ELECTROPLATING
RCM
NICKEL PHOSPHOROUS
LAMINATION
OHMEGAPLY®
LAMINATE
2
Sheet Resistivity Offerings Sheet
Material
Resistivity Tolerance
10 Ω/□
3%
25 Ω/…
50 Ω/…
100 Ω/…
250 Ω/…
5%
5%
5%
10%
Typical
Applications
Developed for series termination for series termination
resistors as ORBIT® (Ohmega Resistor Built In Trace) and also used for other applications, like flexible heaters
Extensively used for series/parallel termination resistors
Used as pullup/pulldown resistors for Used
as pullup/pulldown resistors for
electronic logic circuits
3
Design Guidelines
Explanation of Ohms‐Per‐Square
Sheet resistivity (stated in Ohms per square) is dimensionless
• A square area of resistive material = sheet resistivity of resistive material
E.g., a 25 Ω/(Ohms/Square) sheet resistance
L1 = W1
L2 = W2
N1 = 1
N2 = 2
R1 = 25 Ohms R2 = 25 Ohms
•
L3 =W3
N3 =3
R3 = 25 Ohms
Resistor value = sheet resistivity x ratio of length to width (R =Rs x L/W)
E.g., at 25 Ω/Sq. sheet resistivity
Length = 0.030” (30 mils)
Width = 0.015 “ (15mils)
Resistor value = 25 Ω/Sq. x (30mils/15mils)
= 25 Ω/Sq. x 2 squares = 50 ohms
4
OhmegaPly ® Parallel Termination Buried Resistors
A. Parallel Trace Termination
A Parallel Termination resistor [R] is selected to match the trace impedance [Zo] and may be taken to GND or Vcc [the Power Supply]. A reflection will occur when the termination resistor [R] does not match the trace impedance [Zo]. Some designers set the termination resistor value somewhat higher then Zo to reduce the amplitude of the value somewhat higher then Z
to reduce the amplitude of the
reflection. 5
OhmegaPly® Parallel Termination Buried Resistors
B. Example layouts and circuits of parallel termination resistor
p
y
p
3‐D Drawing of parallel termination resistors in a BGA package
•
•
•
Resistors are terminated in the ground/power plane
Ground plane supports heat dissipation and provides shielding
Ground plane supports heat dissipation and provides shielding
Resistor size can be as small as 7mils x 7mils (limited by resistor power and tolerance requirements)
6
C. Typical layout for parallel termination resistors
1)
44 ohm parallel termination resistors in a BGA
Resistor length = 35 mils
Resistor width = 20 mils
Resistor squares = 35mils/20mils = 1.75 squares
l/
l
Resistance = 25 ohm/square X 1.75 squares
= 44 ohms Resistor
7
Example of Parallel Resistor Layout
2))
1.27mm.
Ø 0.013in.
Resistor Area = 0.010" x 0.0188"
= 0.000188in2
Applied Voltages
Ø 0.024in.
Ø 0.034in.
Power = (1.5V)2 / 47 ohms
= 47.87 mW
Power Density per resistor element
= 47.87 mW / 0.000188 in2
= 254.64Watts per in2
d
rie tor
Bu sis
e
R
d
rie tor
Bu sis
e
R
0.0103in.
.
in
40
00
0.
n.
0i
01
0.
n.
5i
.
00
in
0.
88
01
0.
1.27mm.
Using 25 ohm / square material
Tolerance:
Preferred: 47 ohm +/- 10%
Acceptable: 47 ohms +/- 15%
Plane
Clearance
d
rie tor
Bu sis
e
R
d
rie tor
Bu sis
e
R
Copper
Pad
All dimension in inches
unless otherwise noted.
47 Ohm Buried Resistor
8
Example of Parallel Resistor Layout
3))
Tolerance:
Preferred: 100 ohm +/- 10%
Acceptable: 100 ohms +/- 15%
Using 100 ohm / square material
0.183in.
Finished Hole
Ø 0.018in.
Drilled Hole
Ø 0.015in.
0.0290in.
Ø 0.030in.
30 x 30
Pad
Plane Clearance
30 x 30
0.0300in.
0.0300in.
0 005" around element
0.005
0.0290in.
0.0580in.
0.0110in.
0.0050in.
Resistor Area = 0.030" x 0.030"
= 0.0009 in2
Applied Voltages
Po er = (1
Power
(1.8V)
8V)2 / 100 ohms
= 32.40 mW
Power Density per resistor element
= 32.40 mW / 0.0009 in2
= 36 Watts per in2
100/100 Ohm Buried Resistor
9
Parallel termination resistors on an inner layer of a PCB
10
OhmegaPly ® Series Termination Buried Resistors
A. Series Trace Termination
Series Termination requires a resistor [R] placed near the source. The Series Termination resistor [R] should be selected so that the combination of the resistor [R] and the output resistance [Zs] of the combination of the resistor [R] and the output resistance [Z
] of the
driver matches the trace impedance [Zo]. 11
OhmegaPly ® Series Termination Buried Resistors
B. Example layouts and circuits of series termination resistor
3‐D Drawing of series termination resistors in a BGA package
•
•
Resistors are terminated on existing layers
Proper layout improves signal integrity and increase performance
12
C. Typical layout for series termination resistors
1)
63 ohms series termination resistors in a BGA
Resistor length = 25 mils
Resistor width = 10 mils
Resistor squares = 25 mils/10 mils = 2.5 squares
Resistance = 25 ohm/square X 2.5 squares
= 63 ohms Resistor
13
Example of Series Resistor Layout
2)
50, 125, 250 & 600 ohms series termination resistors using 25 ohms/square OhmegaPly ®
14
Example of Series Resistor Layout
3)
Copper pads
50 ohms series termination resistors ina BGA package using 50 ohms/square OhmegaPly ®
15
Series termination resistors for telecom switching card
16
Series Termination Buried Resistors Using ORBIT ®
(Ohmega Resistor Built in Trace)
ORBIT ® uses the trace itself for the resistor, and therefore, requires no additional board area, thereby enabling higher I/O
thereby enabling higher I/O and component density and reduced form factor.
With resistor built in trace, the CAD layout is simplified by the elimination of the resistor terminations
ORBIT® as series terminating resistors.
17
Enlargement of ORBIT® as series terminating resistors.
18
Fan‐out layout of series termination in a BGA package
19
Fan‐out of series termination resistors in a HDI layout with Micro BGA 20
Optimum Design
A. Thermal/Mechanical Isolation The primary purpose of thermal or mechanical isolation is to reduce stress due to the flow of heat from a plated through via or surface mount pad during soldering, process, reflow, hot air, etc
Secondarily, it also acts as a mechanical isolation preventing resistance change during via drilling and/or x,y and z axis dimensional movement of the PCB. The recommended thermal isolation distance from the edge of the plated through hole to the resistor element is 10 mils, and 5mils for laser drill microvias.
0.010”
Distance for laser drill
0.005”
THERMAL ISOLATION
COPPER PAD
RESISTOR ELEMENT
PLATED THROUGH HOLE
Thermal/mechanical isolation
21
1) Thermal Isolation Isolation distance of OhmegaPly resistors from the edge of the drill hole to the resistor elements
An inner layer showing thermal isolation of OhmegaPly® resistors 22
2) Mechanical Isolation A server backplane showing mechanical isolation of OhmegaPly® resistors due to the use of press‐fit connectors
23
B. OhmegaPly® Power Dissipation vs. Area of Element at 25 C Ambient
For resistor area larger than 1100 mil2, the recommended power dissipation at 25 °C ambient is as follows:
POWER DENSITY OF 10-250 OHM/SQ. MATERIAL VERSUS
DIFFERENT RESISTOR AREA AT 25C AMBIENT
1.2000
10 Ω/… 0.187+ MilliWatts/mil2
25 Ω/… 0.150+ MilliWatts/mil2
50 Ω/… 0.138+ MilliWatts/mil2
100 Ω/… 0.100+ MilliWatts/mil2
250 Ω/… 0.090+ MilliWatts/mil
250 Ω/…
0.090+ MilliWatts/mil2
10 Ohm/Sq.
P ow er Density (m W /m il 2 )
1.0000
25 Ohm/Sq.
y = 76.5x -0.87
50 Ohm/Sq.
0.8000
y = 61.2x -0.87
100 Ohm/Sq.
250 Ohs/Sq.
y = 54.5x -0.87
0.6000
y = 45.9x
45 9x -0.87
0.4000
y = 39.7x -0.87
0.2000
0.0000
0
100
200
300
400
500
600
700
800
900
1000
1100
Maximum power dissipation depends on the ambient temperature, resistor element size, and laminate/circuit board thermal properties. Dissipation improves with the use of natural heat sinks such as ground and power planes. Typical power dissipation for most PRT resistor designs operating at an ambient of less than 70 °C
less than 70 C is approximately 1/10 is approximately 1/10
to 1/8 watt.
2
Resistor Area (mil )
The recommended power dissipation of small resistor area (less e eco
e ded po e d ss pat o of s a es sto a ea ( ess
than 1100 mil2) at 25 °C ambient
24
Determine and Recommend Resistor Sizes Using the OhmegaPly®
Spreadsheet Program
A - DESIGN SPECIFICATION
Please enter the resistance value (R ) in Ohm, power rating (P) in milliWatt, and maximum tolerance
(t ) in percent for each desired resistor (R 1 , R 2 , R 3 , R 4 & R 5 ) in table 1 below, and exit the cell
to allow the program performs the calculations.
R1
Resistance Value (R) in Ohm
Power Rating (P) in mW
Maximum Tolerance (t) in %
R2
10
20
7
R3
25
62
11
50
65
15
R4
R5
100
125
15
250
250
20
Table 1. For designer to enter the resistance, power rating and percent tolerance values of desired resistors
B - RECOMMENDED MINIMUM WIDTH AND LENGTH OF DESIRED RESISTORS
Sheet
R1
R2
Resistivities
W1
(Ohm/Sq.)
(Mil)
(Mil)
10
25
50
100
35.0
123.0
210 0
210.0
385.0
35.0
49.2
42 0
42.0
38.5
250
607.0
24.3
L2
W2
t*
t*
tt*
t*
P*
R3
L2
(Mil)
(Mil)
12.0
23.0
35 0
35.0
58.0
30.0
23.0
17 5
17.5
14.5
770.0
77.0
W3
t*
t*
tt*
t*
t*
R4
L3
(Mil)
(Mil)
7.0
11.0
16 0
16.0
28.0
35.0
22.0
16 0
16.0
14.0
84.0
16.8
W4
t*
t*
P*
P
P*
t*
R5
L4
(Mil)
(Mil)
7.0
13.0
20 0
20.0
35.0
70.0
52.0
40 0
40.0
35.0
59.0
23.6
W5
L5
(Mil)
P*
P*
P*
P
P*
P*
(Mil)
7.0
13.0
19 0
19.0
32.0
175.0
130.0
95 0
95.0
80.0
53.0
53.0
P*
P*
P*
P
P*
P*
Table 2. The recommended minimum width and length for each desired resistor which is calculated by the program base on the given
values by the designer in table 1.
C - RECOMMENDED RESISTOR FOOTPRINTS
Rs
R2
R3
50
100
Bar Type
Partial Square
Partial Square
Partial Square
Bar Type
Bar Type
Partial Square
Partial Square
Bar Type
Bar Type
Bar Type
Partial Square
Bar Type
Bar Type
Bar Type
Bar Type
Serpentine
Bar Type
Bar Type
Bar Type
250
Partial Square
Partial Square
Partial Square
Partial Square
Bar Type
10
25
R1
R4
R5
Table 3. The recommended resistor footprints for different type of sheet resistivities
25
Parametric Design in Supermax® ECAD of Mentor Graphics
Once a resistor is set to be an embedded resistor, the system automatically syntheses multiple permutations of the resistor. For each resistor, the resulting power handling and dimensions are shown and the designer may choose the desired permutation by clicking in the spreadsheet or use the automatic optimization functions to optimize either on total area or by the 26
number of resistance layers needed.
Parametric Design in Supermax® ECAD of Mentor Graphics
Advanced capabilities for embedding passive components Supermax ECAD provides an effective platform for the design of embedded passive components – resistors, capacitors, inductiors and transformers.
•
•
•
•
•
•
•
•
Create and place embedded components on any layer Edit components online
Edit components online Automatic synthesis of resistors and capacitors Resistor types: L‐shape, serpentine, tophat and rectangle Automatic generation of all production documents Firmly integrated with common schematic y
g
environments such as Mentor Graphics® Design Architect® and DxDesigner™ Integrated with analysis tools and virtual prototyping environments Read and write standard formats such as GDS Design Rule Check (DRC)
Since embedded passives are not standard discrete compo‐nents but are, in fact, DC short circuits, DRC functions need to recognize the difference between a DC
functions need to recognize the difference between a DC short circuit and an AC short circuit. With Supermax ECAD, design specifica‐tions are met with an extensive rules set and online DRC of electrical and manufacturing rules. In addition, Supermax ECAD has online verification of signal g y
,
,
,
integrity rules, clear‐ance rules, trace resistance, impedance and propagation delays. 27
Standard CAD Layout Tools
Ohmega resistor design with standard CAD tools
Instructions available for: 1. Mentor Boardstation
2. Allegro
3. Intergraph, Classic
4. PAD Power PCB
Used in conjunction with the OhmegaPly® Excel program, these
Used in conjunction with the OhmegaPly
Excel program these
methods achieved full logic‐DRC resistor controlled schematic
or net list level.
or net list level.
28
References
Please contact Ohmega Technologies (phone: 310‐559‐4400) or e‐mail [email protected] for a copy of the following information:
A. General Ohmega Design Guide
B. OhmegaPly ® Spreadsheet Design Program in Excel
C. Instructions for Design of OhmegaPly ® resistors with standard
CAD tools
29
OHMEGA TECHNOLOGIES, INC.
4031 ELENDA STREET
CULVER CITY, CA 90232‐3799
PHONE: (310)559‐4400
FAX: (310)837‐5268
(
)
WEB SITE: http://www.ohmega.com
Version 1.0
April 2010
Copyright © 20010 Ohmega Technologies, Inc.
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