White Paper-Printed Circuit Board Embedded Thin Film Resistors
White Paper-Printed Circuit Board Embedded Thin Film Resistors
White Paper-Printed Circuit Board Embedded Thin Film Resistors
2
Why use Embedded Resistors?
• Density improvement—free up board area or reduce board
size with elimination of discrete resistors
• Improved reliability with reduction in solder joints
• Elimination of parasitic inductance in power dividers
• Critical signal measurements to meet fast rise times and
reduce signal delay
• Placement of a termination resistor very close to the drive
line
• Very small element sizes with subtractive PCB print/etch
• EMI improvement and improved fidelity in conjunction with
a planar capacitor as an RC filter in MEMs microphone
modules
• Embedded or integral heaters at board level
3
Thin Film Resistive Material Manufacturing
4
NiP Sheet Resistivity Offerings
Sheet Material
Resistivity Tolerance Typical Applications
(Ω/□) (%)
Series termination, impedance
10 3
matching, planar heaters
25 5
Series/parallel termination
40 5
resistors, power dividers, filters
50 5
100 5 Pull-up/pull-down resistors
250 10 High ohmic applications
5
Basic Design Overview
• Sheet resistivity, stated in Ohms per square is dimensionless
• A square area of resistive material equals the sheet resistivity of material
Ω
• 25 ohms per square (■) sheet resistance
• Resistor value = sheet resistivity X ratio of element length to width
𝐿 𝐿
• 𝑅 = 𝑅𝑠 × 𝑊 ; where 𝑊 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑞𝑢𝑎𝑟𝑒𝑠 𝑁
• For example:
• Sheet resistivity (Rs) = 25 Ω/□
• Length = 0.030” (30 mils)
• Width = 0.015” (15 mil)
Ω 30 𝑚𝑖𝑙𝑠
• 𝑅 = 25 × ∎
∎ 15 𝑚𝑖𝑙𝑠
• 𝑅 = 50Ω
6
Sheet Resistivity (Rs) Adjustments for PTFE Substrates
• Lamination of NiP to PTFE substrates results in a
one time shift in nominal sheet resistivity:
• 25 ohm per square → 28 ohm per square
• 50 ohm per square → 60 ohm per square
• 100 ohm per square → 140 ohm per square
• For designs requiring a PTFE substrate, the
modified sheet resistivity should be used when
calculating resistor footprints.
7
Ohms Per Square
• Pull-up/down and termination resistors military/aerospace board
8
Ohms Per Square
• Sample Circuit 50 ohm per square on Duroid 6202PR
9
PCB Processing of NiP Resistive Conductive Material
• Step 1: Apply Photoresist to Laminate
10
PCB Processing of NiP Resistive Conductive Material
• Step 2: Print and Develop Composite Image
11
PCB Processing of NiP Resistive Conductive Material
• Step 3: Etch Unwanted Copper Using Any
Conventional Etchant (1st etch)
12
PCB Processing of NiP Resistive Conductive Material
• Step 4: Etch Unwanted Resistive Material with
Copper Sulfate Solution (2nd etching process)
13
PCB Processing of NiP Resistive Conductive Material
• Step 5: Strip Photoresist
14
PCB Processing of NiP Resistive Conductive Material
• Step 6: Apply Photoresist, Print and Develop
Conductor Protect Image (2nd print)
15
PCB Processing of NiP Resistive Conductive Material
• Step 7: Etch Away Copper Over the Designed
Resistor Using a Selective Alkaline Etchant (3rd etch)
16
PCB Processing of NiP Resistive Conductive Material
• Step 8: Strip Photoresist
17
Two Print Artwork PCB Processing
Artwork layout
• NiP resistor processing consists of two prints:
• 1st print – COMPOSITE image of conductors and resistors
• 2nd print – RESISTOR DEFINE image of resistor elements
COPPER
PAD
18
NiP Resistive Material in RF Applications
• Provides greater packaging densities
• Eliminates resistor assembly
• Eliminates solder joints
• Weight savings
• Reduction in parasitic inductances and
capacitances
• Excellent stability beyond 70 GHz
• Low profile copper for low insertion loss
19
NiP Resistive Material in RF Applications
20
Performance Benefit of NiP Planer Resistor
• Reduction in parasitic capacitance and inductance
compared to surface mount components.
• Reduce metal-to-metal transitions associated with chip
resistors
• Reduce vias on critical nets
21
NiP Resistors in Microwave Applications
22
NiP Resistors in Microwave Applications
0.026” x 0.0145
Enlargement of a four-up array 16-way power divider with 50 /sq NiP resistors
23
NiP Resistor Designs in Space Applications
24
Globalstar Antenna – NiP Resistor Inner Layer
25
NiP Resistor Designs in Military/Aerospace Applications
26
NiP Resistive Material in R-Cards and Absorbers
• Can be laminated to a variety of substrate materials
with different permittivities
• Create repetitive, planar patterns using standard
photolithography techniques (subtractive
print/etch)
• Cost reduction
• Weight savings (reduced thicknesses)
• Increased bandwidth and improved performance
covering wider angles of incidence
27
NiP Resistors in RF Electromagnetic Absorbers and R-cards
28
NiP Resistors in RF Electromagnetic Absorbers and R-cards
29
NiP Resistive Conductive Material in Sensors
• Increased PCB density (small element sizes)
• Reduced PCB thickness (eliminate SMT-R)
• Reduced assembly (resistor built into PCB)
• Improved Reliability (elimination of solder joints)
• Improved electrical performance (reduced EMI)
• Cost savings (replacement of discrete SMT-R)
30
NiP Resistors in MEMs Microphone Sensor
31
NiP Resistors in MEMs Microphone Sensor
32
NiP Resistors in MEMs Microphone Sensor
2.5”
Consumer Electronics
3.5”
MEMs Microphones
33
NiP Resistor Reliability
• Researchers at Alcatel Bell tested NiP resistors for broadband (45 MHz-5 GHz)
telecom applications to compare the reliability of NiP resistors to 0805 discrete
thick film chip resistors rated at 125mW. The NiP resistors were as good as, or
better than, the chip resistor in all performed tests.
Measured ΔR Thick Film Chip
Type of Test Ohmega Specifications
(Alcatel Tested) (0805)
After 21 days:
• 0.22% for 25 Ohm/sq.
Humidity Test • 0.07% for 100 Ohm/sq.
After 10 days:
• 0.10% for 250 Ohm/sq. After 56 days:
Temp: 40°C • 0.5% for 25 Ohm/sq.
After 56 days: ≤ ± 1.5%
RH: 93% • 1.0% for 100 Ohm/sq.
• 0.74% for 25 Ohm/sq.
• 0.14% for 100 Ohm/sq.
• 0.22% for 250 Ohm/sq.
34
NiP Resistor Reliability
• Dassault Electronique (Thales) did a 2 year study of NiP resistors for an active phased array
antenna (X-band). The resistors were constructed on Rogers RT Duroid® 6002 substrate and
fusion bonded inside a multilayer package. The NiP resistors were selected over printed polymer
ink and chip resistors.
Method Result
Etching Tolerance (%) 5
Minimum Resistor Width (um) 200
Tolerance After Fusion Bonding (%) 7
Influence of NiP Layer on Microwave
Negligible
Properties
Thermal Cycle (% ΔR) • Microstrip 2%
• -55°C to 125°C, 500 cycles • Stripline 3%
Thermal Coefficient of Resistance (% ΔR) • Microstrip +/- 2%
• -55°C to 125°C • Stripline +/- 3%
Power (mW) 300
2-Port Power Divider Environmental
Stress Test (% ΔR)
• Thermal Cycle: -55°C to 125°C, 500 cycles Negligible
• High Temperature Storage: 125°C, 500 hours
• Static Humidity: 40°C, 95% RH, 40 days
• Salt Spray: 48 hours
35
NiP Resistor Reliability
• NiP for lead-free assembly. Highly Accelerated Thermal
Shock Test (HATS)
• -40°C to 145°C
• 1000 cycles
• 10.85 minutes per cycle
Resistor Network % ΔR
15 Coupons per Resistor network
1 0.20
2 0.15
3 0.20
4 0.17
36
NiP Resistor Reliability
• Stability over long term continuous operation
37
NiP Resistor Reliability
• Application shows a heater used to bring the X-Ray Spectrometer (XRS)
biasing and pre-amplification electronics to -50 degrees Celsius in the
Mars Beagle 2 Lander.
38
Summary
• NiP thin film resistive material used extensively in
RF and MEMs designs
• Improved package densities
• Improved electrical performance
• Improved reliability
• Standard subtractive PCB processing
• Growing applications in IC packaging, IOT sensor
technologies, 5G and DDR4 memory devices
39
OHMEGA TECHNOLOGIES, INC.
4031 ELENDA STREET
PHONE: (310)559-4400
FAX: (310)837-5268
40