High Reliability PCB

Definition of Reliability

  • Reliability is the ability of an apparatus, machine, or system to consistently perform its intended or required function or mission, on demand and without degradation or failure.

Military standard definition of reliability

  • Reliability is the probability that an item will perform a required function without failure under stated conditions for a stated period of time.

Examples of High Reliability Applications

High Reliability PCB

Drones – IPC Class 3 – High Reliability

High Reliability PCB

Oil Wells – Extreme High Reliability PCB

Institute for Interconnecting and Packaging Electronic Circuits (IPC) Develops and distributes standards to PCB designers, users, suppliers, and fabricators

  • Class 1
    • Consumer products, including TV sets, toys, entertainment electronics, and non-critical consumer or industrial control devices
  • Class 2
    • General industrial, including computers, telecom equipment, business machines, and non-critical military applications
  • Class 3
    • High reliability, including equipment where continued performance is critical, life support & Military
  • Class 3A
    • Performance Specification for Space & Military IPC 6011/6012 Classification
  • Type 1
    • Single–Sided
  • Type 2
    • Double-Sided
  • Type 3
    • Multilayer without blind & buried vias
    • High Reliability
  • Type 4
    • Multilayer with blind & buried vias
    • High Reliability Advanced
  • Type 5
    • Copper core Multilayer without blind & buried vias
  • Type 6
    • Copper core Multilayer with blind & buried vias

MIL-PRF-55110G – Military Performance Specification

  • Type 1
    • Single–Sided
  • Type 2
  • Type 3 – High Reliability Advanced
    • Multilayer, includes metal core and blind & buried vias

MIL-PRF-31032/5 – Military Performance Specification

  • Type 1
    • Single–Sided
  • Type 2
    • Double-Sided
  • Type 3 – High Reliability
    • Rigid Multilayer without blind or buried vias
  • Type 4 – High Reliability Advanced
    • Rigid Multilayer with blind & buried vias
  • Type 5
    • Rigid Multilayer without blind or buried vias with metal core or metal backing external heat-sink
  • Type 6
    • Rigid Multilayer with blind or buried vias with metal core or metal backing external heat-sink

Aspect Ratio: Through Holes and Microvia

  • Aspect Ratio Drives the Drill Diameter (10:1 Standard)
  • Increasing layer counts and reduced hole diameters are driving Aspect Ratios beyond limits of standard electroplating
  • High Aspect Ratio requires Complex Waveform Pulse Plating
  • Copper deposition is enhanced By modifying the plating chemistry In the reverse current cycle to Reduce copper deposition in high Current density areas of the hole Barrel, resulting in uniform plating

Mechanically drilled through hole Via

Mechanically drilled through hole that will be used to penetrate the entire thickness of the PCB or a through hole that will be used in a mechanically drilled sub-lamination used to form blind or buried vias.  In this configuration the depth of the hole is measured from the surface of the external copper layers.  In this case if the hole diameter was 0.010” and the depth was 0.093” the Aspect Ratio would be 9.3 to 1

Mechanically drilled through hole Via

Mechanically drilled through hole Via

Laser drilled microvias

Laser drilled microvias are a controlled depth hole that terminates on a copper layer.   As a result, the depth of the hole is calculated from the top of the terminating layer to the top of the copper foil layer on the hole entrance.  In this case if the hole diameter was 0.006” and the depth was 0.003” the Aspect Ratio would be 0.5 to 1

Laser drilled microvias

Laser drilled microvias

Design rules for Microvia build-up layers

  • Build-up dielectric layers must be balanced on either side of the sub-lamination
  • Build-up dielectric layers are generally 0.0025” to 0.003” thick
  • The recommended total number of lamination cycles that any one part of the structure should experience is 3 and 4 – 5 for advanced structures
  • Microvias stacked on buried mechanical vias should be avoided due to wrap plating requirements and excessive stress on thicker substrates
  • Solid copper mechanically drilled via’s can be used on thin sub-lamination cores in place of wrap plating

 BGA Design Guidelines for High Reliability PCB

1.27 mm BGA – IPC 6012 Class 3 – External Layer

1.27 mm BGA-DFM

1.27 mm BGA-DFM

1.27 mm BGA – IPC 6012 Class 3 – Internal Layer

1.27 mm BGA-DFM

1.27 mm BGA-DFM

1.27 mm BGA – IPC 6012 Class 3 – Internal Layer

1.27 mm BGA-DFM

1.27 mm BGA-DFM

1.27 mm BGA – IPC 6012 Class 3

0.035” (0.889 mm) clearance

1.27 mm BGA-DFM

1.27 mm BGA-DFM

1 mm BGA – IPC 6012 Class 3 – External Layer

1 mm BGA-DFM

1 mm BGA-DFM

1.27 mm BGA – IPC 6012 Class 3 – Internal Layer

1 mm BGA-DFM

1 mm BGA-DFM

1 mm BGA – IPC 6012 Class 3 – Internal Layer

1 mm BGA-DFM

1 mm BGA-DFM

0.8 mm BGA – Microvia Technology

0.8 mm BGA-DFM

0.8 mm BGA-DFM

0.8 mm BGA – Microvia Via-in-Pad Technology

0.8 mm BGA-DFM

0.8mm BGA DFM

PCB Integrity and Reliability evaluation

  • Interconnect Stress Test (IST)

Interconnect Stress Test (IST) is an accelerated stress test method used to evaluate the integrity of the Printed Circuit Board (PCB) interconnect structure.

  • Highly Accelerated Thermal Shock (HATS)

The HATS system’s programmable self-contained machine will do all the common reliability cycles, with a range from -55°C to +145°C in air-to-air mode.

PCB Design Considerations for high reliability PCB

  • The key to a successful Design is the right combination of trace width & space, drill diameter, pad diameter, anti-pad, and aspect ratio. This will maximize routing density, improve electrical characteristics and allows the PCB to be fabricated with high yields for the lowest cost in a timely manner.
  • Maintain robust Trace & Space (0.005” trace & space)
  • 10:1 aspect ratio or lower
  • Min of 0.0012” copper on the wall of plated holes (Class 3A avg 0.0015”)
  • Single lamination cycle (symmetrical construction – copper – laminate – prepreg)
  • Utilize Solid Copper Microvias if required (Via-in-Pad OK)
  • Maintain 70% copper density or greater (add copper pour if needed)
  • Eliminate through-hole via-in-Pad with non-conductive fill and plate
  • Choose the Right PCB Material for your application
  • Impedance Tolerance 10%
  • IST & HATS Test to determine relative long term reliability
  • Keep it Simple  (Different Levels for High Reliability Design)

Cerra Systems Printed Circuit Board Fabrication capabilities support high-frequency PCB, High-temperature Boards, Thick PCB, ultra-thin PCB, heavy copper PCB, Metal Core PCB, HDI boards with Blind Vias, Buried Vias, Micro Vias, Embedded passives, bonded heat sink, Impedance Control, Depth control drilling, Back drilling, Edge Plated PCB, Bump Pads, cavity with ledge, Via on pad and stacked micro-Via technology.

CerraSystems – http://cerrasystems.com

HDI PCB ,  Rigid Flex PCB,  RF PCB 

Electronics Manufacturing Partners:

Argus Systems (AESPL) –  www.sysargus.com

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