September 2020 FAQ: PEM

Integra Technologies has more experience with PEM quals than any other test lab. The following are some of the frequently asked questions:

Q:  What is a PEM?

pemA:  Plastic encapsulated IC’s or Microcircuits are commonly referred to as PEMs.  Plastic encapsulated Transistors and Diodes are typically referenced as PETs and PEDs respectively.

Q:  Why do companies use PEMs?

A:  The main reasons are

  • Primarily to lower costs and accelerate time to market because:
  • Higher volume/more cost-effective production
  • Shorter lead times – many products off-the-shelf
  • Greater product variety
  • Mechanically more rugged
  • Lighter weight - available in smaller/thinner packages

Q:  What are the potential concerns with PEMs in an Aerospace and Defense system?

A: The main potential concerns are:

  • PEMs have predominately been designed for commercial and industrial applications – not Aerospace and Defense (A&D).
  • Higher military temperature ranges are not generally available (except EP)
  • Typical PEMs are COTs and screening by OCM are not always as stringent as A&D end applications require.
  • Qualifications are typically at the inception of product release and is not lot-by-lot.
  • Qualifications are typically not sequential as used by A&D.
  • Reliability of plastic packages could vary dramatically from supplier to supplier.
  • Copper bond wire PEMS are known to have Reliability concerns if not properly manufactured

Q:  What are typical PEM failure modes?

A:  Typical failure modes are

  • CTE mismatch between molding compound and mase material as well as
  • Pop corning of plastic package
  • Delamination
  • Die attach voids
  • Cracked package & cracked die
  • Wire breaks & wire lift
  • Corrosion
  • Contamination
  • Moisture ingression / Current leakage
  • Cracked passivation

dpa-1Q:  What are some key considerations in a PEM qual plan?

A:  Perform a detailed construction analysis or DPA on package before the qual. You will learn a lot of package weakness data before start of qual. Canned qual plans can be a good start but additional device specific information such as application and original data from the manufacturer will help.

Q:  What are some PEM qual plans?

A:  Some of the plans:

  • SAE Standards
    • AS6294/1 for Space PEMs and AS9294/2 for Military PEMs
    • AS6294/3 for Space PEDs and AS6294/4 for Military PEDs
  • NASA Standards
    • PEM-INST-001 (NASA Goddard)
    • MSFC-STD-3012 (Marshal Space Flight Center)
  • Mil Std
    • MIL-PRF-38535: General Specification for Integrated Circuits (Microcircuits)
      • Class N
      • Class Y (Flip Chip)
    • MIL-PRF-38534: General Specification for Hybrids
  • AEC (Automotive)
    • AEC- Q100 – Microcircuits Quals
    • AEC - Q101: Discrete Semiconductor Quals
    • AEC-Q006: Copper Bond Wire Quals

Q:  What is an example of a PEM Qual Plan?

A:  The following is an example of a PEM Qual Plan

  • External visual and serialization: Qty=32
  • Baseline SAM: Qty: 32
  • Pre-Conditioning: Qty=32
    • Moisture soak per appropriate MSL Level
    • Reflow
  • Electrical Testing at 25C, min and max operating temp; Qty=32
  • Sub-Group 1 Qual: Qty=22
    • 125C Life Test for 1000 or 1500 hours
    • Electrical testing at 25C, min and max operating temp
    • Temp Cycle; 200 or 500 cycles
    • Electrical testing at 25C, min and max operating temp
    • SAM: 22 units
    • DPA: 5 units
  • Subgroup 2 Qual: Qty:10
    • Biased or unbiased HAST; 96 hours at 130C/85%RH
    • Electrical testing at 25C, min and max operating temp