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Cordwood electronic packaging

Don Blanchet
Don Blanchet

This document discusses cordwood discrete component electronic packaging used in the 1950s-1960s. Cordwood modules involved stacking electronic components vertically in a cylindrical housing using insulating standoffs, allowing for high packaging density. Early implementations like guidance electronics in missiles had very short service lives due to high vibration levels from tactical use. Modifications like adding mounting feet and spacers could significantly increase the first modal frequency and reduce stresses, resulting in an estimated service life of over 175 hours for applications like tactical jet fighters.

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CORDWOOD DISCRETE COMPONENT ELECTRONIC PACKAGING 1950S -60S HOW DID IT STAND UP TO MILITARY VIBRATION LEVELS ? REV A 1/29/18 D. BLANCHET 3B ASSOCIATES 23 ROCKY HILL RD. BURLINGTON, MA 01803 781-272-7057 DWB3298@OUTLOOK.COM
IN THE YEARS PRIOR TO THE WIDESPREAD USE OF THE INTEGRATED CIRCUIT AND MULTILAYER PWBS Printed wiring boards were crude low density with single or 2 sided traces. Trough holes connected with soldered wires or pressed in eyelets. Electronic circuit elements were in single discrete form usually with axial connection leads. Point to point wiring was often used implemented with manual soldering. Heat density was low and natural convection cooling was usually sufficient. High power parts such as those located in power supplies often had individual heatsinks attached. High Packaging density was often achieved through the use of a technique known as CORDWOOD MODULES.
Early Sparrow Missile Guidance Electronics Hinged cylindrical aluminum platters, Pressed in insulating standoffs Some thin pwbs single trace layers Point-to-point wiring interconnect. VERY SHORT SERVICE LIFE TACTICAL WEAPON SYSTEM
AVIONICS
FEA SOLID MODEL TYPICAL CORDWOOD BENCH DESIGN Breadboards & Brassboards Used for bench Testing and debugging Were often used In tactical Prototype aircraft
SIMULATION MESH
RANDOM VIBRATION PROFILES TACTICAL JET F15
FATIGUE LIFE NON FERROUS COMPONENT LEADS 10,000 psi
BASELINE FIRST MODAL FREQUENCY 123 HZ
RESULTS: MAXIMUM DISPLACEMENT .042 INCHES
RESULTS: MAXIMUM STRESS , 6250 PSI
IN SERVICE LIFE ESTIMATE JET FIGHTER MAX VIBRATION ENVELOPE @ 6250 psi 3 sigma lead bending stress ---- approx. 1e06 cycles to failure @ 123 hz resonance (1e06) / (123) = 8130 seconds 8130 sec / 3600 sec/hr = 2.25 hours
SIMPLE MODIFICATIONS TO INCREASE SERVICE LIFE Add 2 Additional Mounting feet Add 4 Hexagonal spacers
FIRST MODAL FREQUENCY RUGGEDIZED = 294 HZ
CONCLUSIONS CASE RESONANT FREQUENCY MAX 3-SIGMA STRESS, PSI IN SERVICE LIFE EXPECTATION HOURS BASELINE DESIGN 123 6250 2.25 RUGGEDIZED 294 4460 175.00

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Cordwood electronic packaging

  • 1. CORDWOOD DISCRETE COMPONENT ELECTRONIC PACKAGING 1950S -60S HOW DID IT STAND UP TO MILITARY VIBRATION LEVELS ? REV A 1/29/18 D. BLANCHET 3B ASSOCIATES 23 ROCKY HILL RD. BURLINGTON, MA 01803 781-272-7057 DWB3298@OUTLOOK.COM
  • 2. IN THE YEARS PRIOR TO THE WIDESPREAD USE OF THE INTEGRATED CIRCUIT AND MULTILAYER PWBS Printed wiring boards were crude low density with single or 2 sided traces. Trough holes connected with soldered wires or pressed in eyelets. Electronic circuit elements were in single discrete form usually with axial connection leads. Point to point wiring was often used implemented with manual soldering. Heat density was low and natural convection cooling was usually sufficient. High power parts such as those located in power supplies often had individual heatsinks attached. High Packaging density was often achieved through the use of a technique known as CORDWOOD MODULES.
  • 3. Early Sparrow Missile Guidance Electronics Hinged cylindrical aluminum platters, Pressed in insulating standoffs Some thin pwbs single trace layers Point-to-point wiring interconnect. VERY SHORT SERVICE LIFE TACTICAL WEAPON SYSTEM
  • 5. FEA SOLID MODEL TYPICAL CORDWOOD BENCH DESIGN Breadboards & Brassboards Used for bench Testing and debugging Were often used In tactical Prototype aircraft
  • 7. RANDOM VIBRATION PROFILES TACTICAL JET F15
  • 8. FATIGUE LIFE NON FERROUS COMPONENT LEADS 10,000 psi
  • 9. BASELINE FIRST MODAL FREQUENCY 123 HZ
  • 12. IN SERVICE LIFE ESTIMATE JET FIGHTER MAX VIBRATION ENVELOPE @ 6250 psi 3 sigma lead bending stress ---- approx. 1e06 cycles to failure @ 123 hz resonance (1e06) / (123) = 8130 seconds 8130 sec / 3600 sec/hr = 2.25 hours
  • 13. SIMPLE MODIFICATIONS TO INCREASE SERVICE LIFE Add 2 Additional Mounting feet Add 4 Hexagonal spacers
  • 14. FIRST MODAL FREQUENCY RUGGEDIZED = 294 HZ
  • 15. CONCLUSIONS CASE RESONANT FREQUENCY MAX 3-SIGMA STRESS, PSI IN SERVICE LIFE EXPECTATION HOURS BASELINE DESIGN 123 6250 2.25 RUGGEDIZED 294 4460 175.00