Workmanship_ExampleOfWorkmanshipRequirements

As an example of Workmanship requirements, let's consider Polymeric Applications Surface Mount and Hand Soldering, Cables and Harnesses and Fiber Optic Harnesses. The following information is extracted from the NSC Quality Engineering Seminar on Workmanship Standard [11].

General Polymeric Applications Surface Mount and Hand Soldering, Cables and Harnesses, Fiber Optic Harnesses

 

 

 

 

 

 

 

 

Figure 1: Workmanship reference images (left and right) [10].

 

Facilities, Tools, and Equipment:

  • Temperature: 24±30C (75±50F), 30% to 70% Relative Humidity (RH)
  • Safety: chemical handling and storage, ESD wrist-straps are not human protection devices
  • Cleanliness: use and maintenance of production area for intended use, no food, control of foreign object debris (FOD), proper storage of hardware in-process and after processing. For polymeric operations silicone operations must be segregated.
  • Tool Calibration: per ANSI/NCSL Z540.1
  • Light Intensity: a minimum of 1077 Lumens per square meter (Lm/m 2 ) (100 foot - candles)
  • Magnification: simultaneous viewing in both eyes, accurate color rendering, shadowless, 1x to 10x magnification
  • ESD Control: language being changed to point to ANSI/ESD S20.20.

 

 

 

 

 

Figure 2: Facilities, Tools, and Equipment (left and right).

 

Personnel Training and Certification:

  • Personnel: Operators, Inspectors, Level B Instructors 
  • Certification: Guarantee employer makes sure that operator, inspector, instructor meets four minimum criteria:
    • Training (biennially) , Vision (biennially) , Competency, Continuous activity <6 months inactivity
  • Local Trainer = Level B Instructor: Local trainers may be used but must be trained by NASA master trainer (at JPL or GSFC school). Course materials will be provided.
  • Courses: Students may take classes at NASA training centers or from a locally employed Level B instructor. Level B courses shall be made available for review and approval on a project-by-project basis.
  • Training for adopted VCS’s
    • IPC J-STD-001xS: Must use IPC-certified trainer. May use one of the two IPC courses available (modular version, or non-modular version). May use “home grown” course. Course material shall be made available for review and approval on a project-by-project\basis.
    • ANSI/ESD S20.20: Must develop a local implementation plan (local = plant). Must train to local plan. ESDA generic courses, SATURN generic course not sufficient for operators, program monitors, instructors.
  • NASA-STD-8739.X to contain 16-page appendix to explain certification and training requirements.

 

Polymeric Applications

  • Polymer Material Processing: material storage, traceability records, batch mixing, witness sample (test specimen), hardness test
  • PWA preparation: cleaning, solvents, cleanliness test, demoisturizing, priming, masking
  • Staking: Tantalum capacitors, wire runs >1”. For all others if part is marked for staking on the drawing, must use 8739.1 requirements.
  • Fastener Staking: applied to fastener, amount defined, thread locking, torque striping
  • Conformal Coating: brushing, spraying, vacuum deposit, dipping, pre-cure thickness measurement, bubbles, bridging, lead interference, UV inspection, FOD
  • Bonding: Bondline thickness must be defined by engineering, squeeze-out control, voiding must be defined by engineering, one lead free for thermistors
  • Encapsulation: (Potting) vacuum degass material, pre-cure inspection of coverage and bubbles, post-cure inspection for large voids, cracks, excess material
  • Quality Requirements Chapter: Every NASA Workmanship Standard contains a requirements summary section for ease of use by inspectors. All “shall’s” are repeated from earlier sections.

Figure 3: Polymeric applications - Stacking.

 

 

 

 

 

 

 

Figure 4: Polymeric applications - Quality Requirements (left and right).

 

Machine and Hand Soldering

  • Tools: Heat source selection and control (soldering iron, hot gas, radiant)
  • Materials: Eutectic solder, rosin flux, control of solder pot alloy quality
  • Cleaning: Clean bare boards, solvents, cleanliness test, demoisturizing
  • Soldering Prep: Solder paste slump and oxidation test, deposition methods (screen, stencil, syringe)
  • Soldering Prep: lead coplanarity, bending tools, thermal shunts, lead tinning, removal of thick gold, lead and PCB defects, shrink sleeve glass-bodied parts, pre-reflow lead position on solder pad, clearance of wire insulation
  • Part Solderability is required
    • Hand-soldered part installation: terminals, wrapped wires, connector contacts, termination on alternate side of part or both sides.
    • Reflow: Process run records, parameter control, post process cleaning
    • Solder Joint Geometry & Surface Appearance: Cracks, overhang/offset, blow holes, flux residue, stress lines, fillet height, coverage/wetting, excess material

 

 

 

Figure 5: Machine and Hand Soldering - Cleaning.

     

    Figure 6: Machine and Hand Soldering - Hand-soldered part installation.

     

    Figure 7: Machine and Hand Soldering - Solder Joint Geometry & Surface Appearance.

     

     

    Cable and Harness

    • Design Considerations: wire gauge selection, redundancy, contact assignments, routing, bend radius, use of splices, use of sealing plugs, potting connectors, signal isolation and use of EMI shielding, use of identifier marking and tags 
    • Processing prep: use of full-sized mock-ups and wiring boards, protection of harness in-process and in storage.
    • Harness Assembly: Lacing cord stitches, tie wraps, dress of fabric braid layer, spiral wrap sleeving, heat shrinkable sleeving.
    • Cable and Wire prep: wire strip, damaged conductors and insulation, wire lay, insulation clearance, pre-tin for solder cups, cable jacket removal
    • Shield prep: ground connections, dress, and crimp rings 
    • Crimp contacts: contact quality, crimp tool type and calibration, contact/conductor combinations, crimp quality check using pull test
    • Connector assembly: contact installation, sealing plugs, cable clamps, contact seating tests. 
    • Splices: several types defined; solder and non-solder
    • Electrical acceptance testing: continuity, insulation resistance, dielectric withstanding voltage, for coax Voltage Standing Wave Ratio (VSWR), and time domain reflectometry (TDR), before and after installation

     

     

     

     

    Figure 8: Cable and Harness - Design Considerations.

     

     

     

     

     

     

     

     

    Figure 9: Cable and Harness - Cable and Wire prep (left and right)

     

    Figure 9: Cable and Harness - Electrical acceptance testing (top-left); Spliced solder (top-right); Spliced non-solder (bottom).

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    Fiber Optic Cables

    • Materials: solvents, selection and use of adhesives, traceability of materials, adhesive storage conditions, shelf life and pot life , chemical strippers 
    • Personal protection: from glass slivers, eye protection, waste disposal
    • Cable prep: removal of moisture, cable jack and buffer preconditioning, cable layer removal processes
    • Fiber end face prep: ferrule quality check, cleave fiber, polish, inspect, cleaning, protection with dust caps
    • Splices: only fusion type allowed for mission hardware, use strength members for stress relief, no loss of tensile strength in cable, optical time domain reflectometry (OTDR) and attenuation testing
    • Design considerations: cable bend radius, use of splice trays, microbending from cable ties, distinguish from RF cables with marking, cable exits coaxially behind connector for at least 2”.
    • Quality inspection: magnification of 50X – 200X, 100X - 200X for end faces, cracks in end face, cracks in epoxy line, fiber pistoning, buffer or jacket shrink, ferrule quality check, cleave fiber, polish, inspect, cleaning.

     

     

    Figure 10: Fiber Optic Cables - Cable sections.

     

    Figure 11: Fiber Optic Cables - Design considerations.

     

     

     

     

     

     

     

     

    Figure 12: Fiber Optic Cables - Quality Inspection.

     

    Let's practice what we learn in this section: