Workmanship_TermsAndDefinitions

To address Workmanship training and issues it is important to have an understanding of some key concepts with respect to Electronics and Qualification. The definitions were taken from the Workmanship Seminar led by Jeannette Plante at NASA in 2011 [10], text was maintained as the original to avoid discrepancies with the following content.

 

Workmanship: Shorthand term for quality rules applied to the assembly of electronic boards and electrical cable harnesses [10]. 

NASA groups fiber optic cable assembly quality and ESD Control with Workmanship. 

PCB: Printed Circuit Board. An electrical board with integrated electrical connections but no electrical parts installed. Treated like an IEEE part; it is an integrated unit. Flex cables are a type of PCB [10].

PWA: Printed Wiring Assembly. A populated PCB. An electronic board with all parts installed. Sometimes called a CCA; circuit card assembly [10]. 

ESD: Electrostatic Discharge. Sudden discharge of electrical potential through readily available ground path. The effect on electronic assemblies can be catastrophic or crippling but visually hard to detect. Crippled parts may pass now and fail later [10].

Solder: A metal alloy with a low melting point used to provide a conductive, long lasting connection between an electrical part lead and the pad of the printed circuit board or between a wire and a connector contact. 63% Tin (Sn) + 37% Lead (Pb) is standard for electronics [10].

Flux: Acid-containing material (organic or inorganic acid) used to remove oxide and residues from soldered surfaces thereby allowing the solder joint to readily form [10].

Staking: Polymeric material used to mechanically tack-bond part bodies to the PCB surface [10].

Conformal Coating: Polymeric material used to thinly coat a PWA to protect it from “bumps and bruises” and conductive debris. Will also retard surface corrosion of PWA exposed metal surfaces [10].

Wire: Single or stranded insulated conductor used alone or in a cable to support a single electrical connection [10].

Cable: Multiple wires bundled together inside an insulated layer used to support multiple electrical connections. Cables are terminated with connectors [10].

Harness: Multiple cables gathered together for the interconnection of subsystems [10].

Jumper wire: (aka “white wire”) Wire used to provide a single electrical connection within a PWA. The termination method is a solder joint [10].

ESD Event Model: Industry standard description of an electrical discharge event using voltage, current, and time or an equivalent RLC circuit [10].

Quality: Measure of an item’s compliance with published performance parameters (form/fit/function). Quality is relative to what the item is intended to do and can be measured. Production lots with high quality are highly uniform [10].

Reliability (1): The probability of failure used within its intended operating environment before its expected operating life has been completed. Reliability is relative to environmental stresses and minimum required life span. Sample size is important [10].

Reliability (2): Is capable of working in the mission environment for the duration of the mission [10].

 

Other uses of these terms:
Quality: item is good or really good 
Reliable: item will not fail

Process Qualification: Quality parameters have been identified, are controlled, and are monitored to ensure that (a) un-screenable defects are not produced in the final item, (b) every item produced has identical quality, (c) scrap is minimized. Prototype runs and destructive tests are used to achieve (a) above. Non-destructive in-line and end-of-line tests and inspections are used to achieve (b) above. Process Qualification ensures that the manufacturing recipe “works” [10].

Product Qualification: Destructive testing used to (a) identify relevant screening tests to achieve high and uniform quality and to (b) demonstrate the capability of the finished item to perform as intended in the application environment for the duration intended. “Generic” qualification test flows may use very wide temperature ranges (e.g. mil-spec) and durations that test to failure. Mission-specific qualification test conditions may not be applicable to other missions (Qualification by Heritage) [10].

Product Qualification ensures that the: Design + Manufacturing Screening = A part that is Not Likely to Fail in the Mission.

 

Procedure: Step-by-step instructions for implementing a manufacturing process. Procedures will include steps that ensure that quality requirements are met. These steps may include use of special fixtures, checking temperature, ESD wrist strap check, in-process measurements, and end-point tests and inspections [10].

Requirement Document: Collection of requirements about that item or process that are applicable to the owners. May include accept/reject/defect criteria [10].

Workmanship Standards are Requirements Documents.

 

Note: Along these definitions there is also a NASA standard definition for product qualification named,  "Space Qualified". This is a marketing term.

 

Let's try to remember each concept and the corresponding definition. Without reading, try to assign each concept to the corresponding definition, review the current content page for clarifications: