NASA-STD-8739.3 Manual Flashcards
4.3. Reliable Soldered Connections a. Stress relief
a. Stress relief should be inherent in the design to avoid detrimental thermal and mechanical stresses on the solder connections
4.3. Reliable Soldered Connections b. Where stress relief is not used
b. Where stress relief is not used, a plated-through hole (PTH) is mandatory.
4.3. Reliable Soldered Connections d. visual inspection of all soldered connections.
d. Parts mounting design requirements shall allow full visual or nondestructive inspection of all soldered connections.
6.1 Facility Cleanliness
6.1 Facility Cleanliness The work area shall be maintained in a clean and orderly condition. Smoking, eating, and drinking in soldering areas and at individual work stations shall not be permitted. Nonessential tools and materials shall not be permitted at the workstation.
6.5 Soldering Tools and Equipment 3. Conductive-Type Irons
- Conductive-Type Irons. Soldering irons shall be of the temperature controlled type, controllable within ±5.5°C (±10°F) of the preselected idling temperature.
7.2 Preparation of Conductors 2. Damage to Insulation.
- Damage to Insulation. After insulation removal, the remaining conductor insulation shall not exhibit any damage such as nicks, cuts, or charring. Conductors with damaged insulation shall not be used. Scuffing from mechanical stripping or slight discoloration from thermal stripping is acceptable.
7.2 Preparation of Conductors 3. Damage to Conductors.
- Damage to Conductors. After removal of the conductor insulation, the conductor shall not be nicked, cut, or scraped to the point that base metal is exposed. Part leads and other conductors that have been reduced in the cross-section area shall not be used. Smooth impression marks (base metal not exposed) resulting from tool holding forces shall not be cause for rejection.
7.2 Preparation of Conductors 4. Wire Lay.
- Wire Lay. If disturbed, the lay of wire strands shall be restored as nearly as possible to the original lay. The conductor shall be cleaned following restoration to the original lay.
7.2 Preparation of Conductors 5. Tinning of Conductors.
- Tinning of Conductors. The portion of stranded or solid conductors or part leads that will eventually become a part of the finished solder connection shall be tinned with solder and cleaned prior to attachment. Immersion of conductors in a solder bath shall not exceed 5 seconds. Liquid flux may be used. The flux shall be applied so that it does not flow under the insulation except for traces carried by wicking. Precautions shall be taken when removing flux with a cleaning solvent to prevent excess solvent from flowing under the conductor insulation
7.2 Preparation of Conductors 5. Tinning of Conductors. a. Hot tinning of solid conductors
a. Hot tinning of solid conductors and part leads should not extend closer than 0.5mm (0.020 inch) to part bodies, end seals, or insulation unless the part configuration and mounting configuration dictate. If closer tinning is required, the part body, end seals, or insulation shall be inspected for damage after tinning and the results recorded (see also paragraph 4.1-3).
7.2 Preparation of Conductors 5. Tinning of Conductors. c. Gold plating
c. Gold plating on all surfaces that become part of finished solder connections shall be removed by two or more successive tinning operations (solder pot or iron), or by other processes demonstrated to have equivalent effectiveness.
7.2 Preparation of Conductors 6. Conductor Tinning Product Control
- Conductor Tinning Product Control. Conductor tinning personnel shall ensure that the tinned surfaces exhibit 100 percent coverage. Wire strands shall be distinguishable.
7.3 Preparation of Printed Wiring Boards, Terminals, and Solder Cups 1. Termination areas
- Termination areas shall have been “tinned” with hot-coated tin-lead solder or hot reflowed electrodeposited tin-lead solder prior to mounting the parts. Final solder terminations shall not be made to any PWB or solder cup that has not had the gold removed from the termination area.
7.3 Preparation of Printed Wiring Boards, Terminals, and Solder Cups 2. Terminals and solder cups
- Terminals and solder cups shall be examined for damage and cleaned prior to the attachment of conductors. Terminals and solder cups shall not be modified to accommodate improper conductor sizes.
7.3 Preparation of Printed Wiring Boards, Terminals, and Solder Cups 3. PWB Preparation
- The PWB’s shall be cleaned and demoisturized within 8 hours prior to their initial exposure to soldering temperatures. The PWB’s may be stored for longer periods of time in a controlled moisture-free atmosphere. Demoisturizing may be accomplished by an oven bake at 93°C (200°F) ±5.5°C (±10°F) for a minimum of 4 hours for a printed wiring assembly (PWA) or 2 hours for a bare PWB, or by a vacuum bake at a lower temperature. The time in and out of the oven or chamber shall be recorded.
CHAPTER 8 - PARTS MOUNTING 1. Stress Relief.
- Stress Relief. Stress relief shall be incorporated, wherever possible, into all leads and conductors terminating in solder connections to provide freedom of movement of part leads or conductors between points of constraint. Leads shall not be temporarily constrained against spring-back force during solder solidification so that the joint is subject to residual stress.
CHAPTER 8 - PARTS MOUNTING1. 2. Part Positioning. a. Parts shall be mounted so that terminations of other parts are not obscured.
a. Parts shall be mounted so that terminations of other parts are not obscured. When this is not possible, interim assembly inspection shall occur to verify that the obscured solder joints meet the requirements herein.
CHAPTER 8 - PARTS MOUNTING1. 2. Part Positioning. b. Parts having conductive cases
b. Parts having conductive cases mounted over printed conductors or which are in close proximity with other conductive materials shall be separated by insulation of suitable thickness. Insulation shall be accomplished so that part identification markings remain visible and legible.
CHAPTER 8 - PARTS MOUNTING1. 3. Visibility of Markings.
- Visibility of Markings. Where possible, parts shall be mounted in such a manner that markings pertaining to value, part type, etc., are visible. For parts marked in such a way that some of the marking will be hidden regardless of the orientation of the part, the following shall be the order of precedence for which markings shall be visible: a. Polarity. b. Traceability code (if applicable). c. Piece part value and type.
CHAPTER 8 - PARTS MOUNTING 4. Glass Encased Parts.
- Glass Encased Parts. Glass encased parts such as diodes, thermistors, or resistors shall be covered with transparent resilient sleeving or other approved material when epoxy material is used for staking, conformal coating, or encapsulating or where damage from other sources is likely. The epoxy material shall not be applied directly to glass.
CHAPTER 8 - PARTS MOUNTING 5. Hookup Wire Support
- Hookup Wire. Hookup wire, solid or stranded, shall be supported by a means other than the solder connections or conformal coating if wire length exceeds 2.54cm (1 inch). Attachment to a surface by staking with resin is considered adequate support.
CHAPTER 8 - PARTS MOUNTING 6. Lead Bending and Cutting. a. Part Lead Support
a. During bending or cutting, part leads shall be supported on the body side to minimize axial stress and avoid damage to seals or internal bonds. The distance from the bend to the end seal shall be approximately equal at each end of the part. The minimum distance from the part body or seal to the start of the bend in a part lead shall be 2 lead diameters for round leads and 0.5mm (0.020 inch) for ribbon leads. The stress relief bend radius shall not be less than the lead diameter or ribbon thickness. The direction of the bend should not cause the identification markings on the mounted part to be obscured. Where the lead is welded (as on a tantalum capacitor) the minimum distance is measured from the weld.
CHAPTER 8 - PARTS MOUNTING 6. Lead Bending and Cutting. b. Part lead forming
b. Part leads shall be formed so that they may be installed into the holes in the PWB without excessive deformation that can stress the part body or end seals.
CHAPTER 8 - PARTS MOUNTING 6. Lead Bending and Cutting. c. Before mounting
c. All leads should be tinned and formed before mounting the part WHERE POSSIBLE, PART LEADS THAT ARE SUBJECT TO STRESS CORROSION CRACKING (E.G. KOVAR LEADS), SHALL BE PREFORMED AND TRIMMED PRIOR TO TINNING.
CHAPTER 8 - PARTS MOUNTING 6. Lead Bending and Cutting. d. Nicks or deformations
d. Whether formed manually or by machine, part leads shall not be mounted if they show evidence of nicks or deformations. Smooth impression marks (base metal not exposed) resulting from tool holding forces shall not be cause for rejection.
CHAPTER 8 - PARTS MOUNTING 6. Lead Bending and Cutting. e. Tempered leads
e. Tempered leads (sometimes referred to as pins) shall not be bent nor formed for mounting purposes since body seals and connections internal to the part may be damaged. Tempered leads or leads with a diameter of 1.27mm (0.05 inch) or more shall not be cut with diagonal cutters or other tools that impart shock to connections internal to the part.
CHAPTER 8 - PARTS MOUNTING 7. Coated Parts
- Coated Parts. Parts shall be mounted so that the insulating coating meniscus applied by the manufacturer on the leads does not enter the mounting hole or soldered connection.
CHAPTER 8 - PARTS MOUNTING 8. Splices.
- Splices. Broken or damaged conductors, part leads, or printed wiring conductors shall not be spliced.
CHAPTER 8 - PARTS MOUNTING 9. Location.
- Location. Part bodies shall not be in contact with soldered terminations.
8.2 Mounting of Terminals 1. General.
- General. Use of terminals shall generally be restricted to situations where parts are expected to be removed and replaced, or where there are other compelling design requirements for their use.
8.2 Mounting of Terminals 1. General. a. Terminals
a. Terminals shall not be used as the interface connections in non-plated through holes (PTH’s). Swaging of terminals shall be performed in a way that does not damage the PWB.
8.2 Mounting of Terminals 1. General. a. Terminals b. After swaging or flaring
b. After swaging or flaring, the rolled area or flange shall be free of circumferential splits or cracks, but may have a maximum of three radial splits or cracks provided that the splits or cracks are separated by at least 90° and do not extend beyond the coiled or flared area of the terminal (Figure 8-1).
8.2 Mounting of Terminals 2. Swage type terminals
- Swage type terminals in non-PTH’s, designed to have the terminal shoulder soldered to the printed wiring conductor, shall be secured to the PWB by a roll swage (Figure 8-2).
8.4 Mounting of Parts to PWB’S 2. Axial Lead Mounting
- Axial Lead Mounting. Axial leaded parts shall be mounted as follows: a. Horizontal Mount. Parts intended for horizontal mounting shall be parallel to, and in contact with, the mounting surface (see Figure 8-6), or as specified in the engineering documentation. Slight angularity is permissible. When parts will be bonded, slight spacing will be acceptable.
8.4 Mounting of Parts to PWB’S b. Vertical Mount (1) Plated-Through Hole (2) Non-Plated-Through Hole
(1) Plated-Through Hole. The end of the part body must be mounted with at least 0.5mm (0.020 inch) to a maximum of 1.27mm (0.050 inches) clearance above the PWB surface or as specified on engineering documentation. The end of the part is defined to include any extensions such as coating meniscus, solder seal, or weld bead (see Figure 8-7A). (2) Non-Plated-Through Hole. The end of the part body may be mounted flush with the PWB surface and shall be terminated with an off-the-pad-lap solder joint. The part shall be staked on the part side of the PWB. The opposite lead shall have two approximate right angle bends (see Figure 8-7B).
- 4 Mounting of Parts to PWB’S
- Radial Lead Mounting.
- Radial Lead Mounting. Plated-through-hole: The part body shall be mounted with at least 0.5mm (0.020 inch) to a maximum of 1.27mm (0.050 inch) and shall allow inspection of the solder joint. The part body includes any extension such as coating meniscus, solder seal or weld bead (see Figure 8-8A). Non-plated-through-hole: The part body may be mounted flush with the PWB surface and terminated with an off-the-pad lap solder joint (See Figure 8-8B).
- 4 Mounting of Parts to PWB’S
- Hole Obstruction.
- Hole Obstruction. Parts shall not be mounted such that they obstruct solder flow or prevent cleaning of the topside termination areas of PTH’s (Figure 8-9).
- 4 Mounting of Parts to PWB’S
- Parts with Leads Terminating on Opposite Sides (of the PWB)
Parts with Leads Terminating on Opposite Sides. Stress relief shall be provided in the part lead between the part body and solder terminations (Figure 8-10). The lead may be terminated by clinch, straight-through, or lap configuration.
- 4 Mounting of Parts to PWB’S
- Parts with Leads Terminating on the Same Side (of the PWB)
- Parts with Leads Terminating on the Same Side. Stress relief shall be provided by forming the part leads at a bend angle to the PWB of not more than 95°nor less than 45° (Figure 8-11).
- 4 Mounting of Parts to PWB’S
- Conductors Terminating on Both Sides (Of the PWB)
- Conductors Terminating on Both Sides. Stress relief shall always be provided in the part lead between the part body and solder termination. When a conductor is used to interconnect opposite sides of a PWB, stress relief or a PTH shall be provided (Figure 8-12).
8.5 Boards Lead Terminations
8.5 Boards Lead Terminations, Printed Wiring Part Lead Terminations. Part leads shall be of the lap, clinched, or straight-through configuration as defined by the engineering documentation and shall be terminated in accordance with paragraphs 8.4-1 through 8.4-3. No more than one item, whether conductor or part lead, shall be inserted in any one hole.
- 5 Boards Lead Terminations, Printed Wiring
- Lapped Terminations Height
- Lapped Terminations. Lapped terminations consist of both round and flat ribbon leads. It is preferred that leads be seated in contact with the termination area for the full length of the foot. Separation between the foot of the lead and the surface of the termination area shall not exceed 0.25mm (0.010 inches) (see Figure 8-13).
- 5 Boards Lead Terminations, Printed Wiring
a. Lapped Round Leads.
a. Lapped Round Leads. The round lead shall overlap the solder pad a minimum of 3.5 times the lead diameter to a maximum of 5.5 times the lead diameter, but in no case shall the length be less than 1.27mm (0.050 inch). The cut-off end of the lead shall be no closer than ½ the lead diameter to the edge of the solder pad. Only that portion of the lead extending to the part body or to another soldered connection shall be beyond the solder pad (Figure 8-14A). For lapped terminations where the part body is on the same side of the PWB as the termination area, a heel fillet is mandatory (Figure 8-14B).
- 5 Boards Lead Terminations, Printed Wiring
b. Lapped Ribbon Leads.
b. Lapped Ribbon Leads. The ribbon lead shall overlap the solder pad a minimum of 3 lead widths to a maximum of 5.5 lead widths. Only that portion of the lead extending to the part body or to another soldered connection shall be beyond the pad. The cut-off end of the lead shall be a minimum of 0.25mm (0.010 inch) from the end of the pad. One edge of the lead may be flush with the edge of the solder pad. There shall be sufficient area around two of the three lead edges to accommodate solder filleting (see Figure 8-15). In instances where ribbon leads are less than 0.5mm (0.020 inch) in width, ribbon overlap shall be no less than 1.27mm (0.050 inch). For lapped terminations where the part body is on the same side of the PWB as the termination area, a heel fillet is mandatory
8.5 Boards Lead Terminations, Printed Wiring
- Clinched Lead Terminations. The length of the clinched portion of conductors and part leads shall be at least ½ the largest dimension of the solder pad or 0.78mm (0.031 inch), whichever is greater. Lead overhang shall not violate minimum electrical spacing requirements. The lead shall be bent in the direction of the longest dimension of the solder pad. If the pad dimensions are not sufficient, the lead shall be bent in the direction of the printed wire path (Figure 8-16). There shall be sufficient solder pad area extending beyond the sides of the lead to accommodate solder filleting. Fully clinched leads are defined as leads bent between 75°and 90° from a vertical line perpendicular to the PWB. Nonbendable leads shall not be clinched.
- 5 Boards Lead Terminations, Printed Wiring
- Straight-Through Lead Terminations.
- Straight-Through Lead Terminations. Part leads terminated straight through the PWB shall extend a minimum of 0.5mm (0.020 inch) and a maximum of 2.29mm (0.090 inch). The minimum lead length shall be determined prior to soldering (actual measurement is not required except for referee purposes). Straight-through leads may be bent up to 30° from a vertical plane to retain parts during the soldering operation (Figure 8-19). Nonbendable leads shall not be bent.
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
1./2. Minimum/Maximum Insulation Clearance.
- Minimum Insulation Clearance. The insulation shall not be imbedded in the solder joint. The contour of the conductor shall not be obscured at the termination end of the insulation. 2. Maximum Insulation Clearance. The insulation clearance shall be less than two wire diameters, including insulation, but in no case shall permit shorting between adjacent conductors. Insulation clearance shall be referenced from the first point of contact of the conductor to the terminal.
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
- Multiple Parallel Entry.
- Multiple Parallel Entry. For multiple parallel entry of conductors to a terminal, insulation clearances need not be equal.
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
- Wrap Orientation. Conductors may be wrapped clockwise or counterclockwise on the terminal and shall continue the curvature of the dress. The conductor shall not interfere with the wrapping of other conductors on the terminal. The curvature of the dress shall not exceed 20° from a perpendicular line from the last point of contact between the conductor and terminal (Figure 9-1).
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
- 2 Turret and Straight Pin Terminals
- a/b. Conductor AWG wrap dimensions
- 2 Turret and Straight Pin Terminals
- Side Route. The side route shall be connected as follows: a. Conductor sizes larger than American Wire Gage (AWG) 26 shall be wrapped a minimum of 1/2 (180°) to a maximum of 3/4 turn (270°) around the post (see Figure 9-2A). NASA-STD-8739.3 December 1997 9-3
b. Conductor sizes AWG 26 and smaller shall be wrapped a minimum of 1/2 turn (180°) but less than one full turn (360°) around the post (see Figure 9-2B).
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
9.2 Turret and Straight Pin Terminals
c/d/e. Turret Guide Slots
c. For turret terminals, all conductors shall be confined to the guide slots (see Figure 9-3A).
d. Conductors shall be maintained in contact with the post for the full curvature of the wrap and the conductor ends shall not extend beyond the base of the terminal.
e. More than one conductor may be installed in a single slot of sufficient height, provided each conductor is wrapped on the terminal post and not on another conductor. 2. Bottom Route. The conductor shall enter the terminal from the bottom, be brought through the side slot at the top, and wrapped as required for side route (Figure 9-3B).
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
- 3 Bifurcated Terminals
- Bottom Route.
9.3 Bifurcated Terminals 1. Bottom Route. Bottom route shall be connected as shown in Figure 9-5. Conductors shall not extend beyond the diameter of the base of the terminal except where physical clearance is adequate for the intended environment or electrical characteristics. When more than one conductor is to be attached, it shall be inserted at the same time but shall be wrapped separately around alternate posts.
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
- 3 Bifurcated Terminals
- Side Route.
- Side and Bottom Route.
- Side Route. Side route shall be connected as follows (Figure 9-6): a. The conductor shall enter the mounting slot perpendicular to the posts. b. A conductor may lay straight through a terminal slot provided the conductor surface remains in contact with the terminal surface (Figure 9-6A). Where conductors are wrapped on a terminal post, they shall wrap a minimum of 90° and a maximum of 180° (1/4 to 1/2 turn); refer to Figure 9-7. c. More than one conductor may be installed on a single post provided each conductor is wrapped on the terminal post and not on another conductor. d. When more than one conductor is connected to a terminal, the direction of bend of each additional conductor shall alternate (Figures 9-6B and D). e. Conductors shall not extend beyond the diameter of the base of the terminal except where physical clearance will not adversely affect environmental or electrical characteristics. 3. Side and Bottom Route. The bottom route shall be installed first as shown in Figure 9-5, then the side route as shown in Figure 9-6, methods B, C, or D.
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
9.4 Hook Terminals Connections
9.4 Hook Terminals Connections to hook terminals shall be as shown in Figure 9-10. The bend to attach conductors to hook terminals shall be a minimum of 1/2 turn (180°) to a maximum of 3/4 turn (270°). Protrusion of the conductor ends shall be controlled to avoid damage to the insulation sleeving. Conductors shall be wrapped directly to the terminal and not on other conductors. When more than one conductor is connected to the terminal, the direction of the bend of each additional conductor shall alternate (Figure 9-10).
CHAPTER 9 - ATTACHMENT OF CONDUCTORS TO TERMINALS
9.5 Pierced Terminals Connections
9.5 Pierced Terminals Connections to pierced terminals shall be as shown in Figure 9-11. The bend to attach conductors to pierced terminals shall be a minimum of 1/4 turn (90°) to a maximum of 1/2 turn (180°). Protrusion of conductor ends shall be controlled to avoid damage to insulation sleeving.
CHAPTER 11 - HAND SOLDERING OF PRINTED WIRING ASSEMBLIES
- 2 Solder Application
- Lap Terminations
- Lap Terminations. a. A heel fillet is mandatory for all single surface lapped solder joints. The heel fillet shall be continuous between the heel of the lead and the termination pad. The heel fillet shall extend beyond the lower bend radius but shall not extend into the upper bend radius (see Figure 11-1)
CHAPTER 11 - HAND SOLDERING OF PRINTED WIRING ASSEMBLIES
- 2 Solder Application
- Lap Terminations
b. Round lead lap terminations require a complete solder fillet around all sides of the lead (see Figure 11-2).
