Copyright © 2009 Ohmega Technologies, Inc.
|
|
Embedded Passives (Resistors/Capacitors) in PCBs
|
|
|
|
Advantages of Embedded Resistors
Electrical Advantages
- Improved line impedance matching Improved line impedance matching
- Shorter signal paths and reduced series inductance
- Reduced cross talk, noise and EMI
PCB Design Advantages
- Increase active component density and reduced form factors
- Improved routing due to elimination of vias
- Board simplification, size reduction and/or densification
Improved Reliability
- Low RTC of < 50 PPM
- Life testing: 100,000 hours < 2% drift at 110°C
- Stable over wide frequencies: tested beyond 40 GHz qy
- Elimination of solder joints
- Testing at inner layer and bare board stage
| |
|
NiP Resistive Material
|
|
|
PCB Processing of the NiP Resistor Alloy
|
|
- STEP 1: Apply Photoresist to Laminate
- STEP 2: Print and Develop Composite Image
- STEP 3: Etch Unwanted Copper Using Any Conventional Etchant (1st etch)
- STEP 4: Etch Unwanted Resistive Material with Copper Sulfate Solution (2nd etching process)
- STEP 5: Strip Photoresist
- STEP 6: Apply Photoresist; Print and Develop Conductor; Protect Image (2nd print)
- STEP 7: Etch Away Copper Over Designed Resistors Using a Selective Alkaline Etchant (3rd etch)
- STEP 8: Strip Photoresist
|
|
Embedded Resistor Testing
- Electrical testing is required to verify correct resistor values
and identify out-of-tolerance resistors
- All resistors should undergo electrical testing at the inner layer
and bare board stage to assure resistor tolerances and facilitate
failure analysis.
- AOI is not a substitute for inner layer electrical test
- Standard electrical test equipment is utilized
Universal bare board tester (bed-of-nails with fixture)
Flying probe tester (fixtureless)
|
|
|
Embedded versus SMT Processes
NiP embedded resistors are created using standard print-and-etch
processes and eliminate the need for discrete resistor placement
and attachment.
Standard PCB print-and-etch process controls and IPC Specs apply to
embedded resistors. Soldering process controls and specifications
do not apply to embedded resistors.
In Military/Aerospace and other critical applications, elimination of
the discrete resistor solder joints improves reliability and yields.
|
|
|
NiP Resistor Reliability
|
|
|
Alcatel
Researchers at Alcatel tested NiP resistors for broadband (45 MHz-5 GHz)
telecom applications to compare the reliability of NiP resistors to 0805
discrete chip resistors rated at 125 mW.
The NiP resistors were as good as,
or better than, the chip resistors
in all performed tests.
|
|
|
Alcatel Design - MLB Inner Layer
Termination and pull-up resistors in an ATM switching card.
|
|
|
Dassault (Thales)
Dassault Electronique did a 2-year study of the NiP resistive material for an active phased array antenna (X-band). The resistors were used in a stripline
configuration on a PTFE substrate. The NiP material was compared to chip
resistors and screen-printed polymer inks. The NiP material was selected for use
due to superior tolerance and stability (compared to printed polymer inks) and
space saving, parasitic reduction, and solder joint removal (compared to chip
resistors).
The results of testing are as follows:
|
|
|
NiP Resistor Reliability
Enlargement of a four-up array 16-way power divider
with 50 ohm/sq OhmegaPly ® resistors.
|
|
|
NiP Resistor Reliability
|
|
|
OhmegaPly ® resistor in microwave
application for Globalstar antenna.
|
Layer stack-up.
|
|
|
NiP Resistor Reliability
Military / Aerospace Organization
Highly Accelerated Thermal Shock Test (HATS)
Pull-up / pull-down resistors in a missile control circuit board
|
|
|
NiP Resistor Reliability
|
|
Embedded NiP Resistors in ESA Mars Express Beagle 2 Lander
|
|
Mars Express orbiter
|
Beagle2 Lander with instruments on its robotic arm
|
|
|
X-Ray Spectrometer with cover
to measure the elements in rocks
|
X-Ray Spectrometer (XRS)
with OhmegaPly ® resistors
|
|
|
Top view of PAW (Position-Adjustable Workbench)
|
OhmegaPly ® resistors in electronic lander PC board
|
|
|
NiP Resistor Reliability
|
|
|
NiP Resistors Embedded in DRAM PCB - FR4 Dielectric for Lead-Free Assembly
NiP Resistors on Inner Layer of DRAM Design
|
|
|
|
Enlargement of Above Design
|
NiP Resistors
|
|
|
NiP Resistor Reliability
Application of NiP Resistors on a Lead-Free Substrate
- Resistive stability after solder float (% delta-R)
- Thermal stress test-to-failure.
- Compare FR4 to a "Lead-Free" laminate.
- Test at T260 20 seconds versus T288 10 seconds.
- Preconditioning; baking versus no-baking
- Failure means resistor becomes unstable or open.
- The result was that the lead-free laminate were
clearly superior at T288, surviving 25 cycles.
|
|
|
NiP Resistor Reliability
|
|
|
Memory board, 10 layers with one layer of 22 ohm resistors, 23 mils x 10 mils.
Built using Double Treat 1/2A 50 ohm NiP resistive material.
The FR-4 PCB used a standard multifunctional epoxy laminate.
The "lead-free" PCB used a phenolic-cured laminate.
Testing per IPC-TM-650, Method 2.4.13.1, baking was performed at 125 deg C.
Embedded Resistor stability is an indicator of the PCB structural integrity.
|
|
|
IPC Standards Development
for Embedded Passives
IPC specifications for embedded passives have been
in development for a number of years. These are:
- IPC-4902 Specifications for Materials for
Embedded Passive Devices
for Printed Boards
- IPC-2227, Sectional Design Standards for
Boards Utilizing Embedded Passive Devices
- IPC-4821 Specification for Embedded Passive Device
Capacitor Materials for Rigid and Multilayer Printed Boards
- IPC-4811 Specifications for Embedded Passive Device Resistor Materials for Rigid and Multilayer Printed Boards
| |
|
|
|
copyright © 2009 Brigitflex, Inc.
|
| |
