Navy Electricity and Electronics Training Series - Historic Naval ...

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Figure 3-12B.—Motorized vacuum/pressure solder removal. PRESSURE MODE.Figure 3-12C.—Motorized vacuum/pressure solder removal. HOT AIR JET MODE.Motorized Vacuum Method.—In the motorized vacuum method, the heated tip is applied to thesolder joint. When melted solder is observed, the vacuum is activated by the technician causing the solderto be withdrawn from the joint and deposited into the chamber. If the lead is preclipped, it may also bedrawn into a holding chamber. To prevent SWEATING (reforming a solder joint) to the side walls of theplated-through hole joint, the lead is "stirred" with the tip while applying the vacuum. This permits coolair to flow into and around the lead and side walls causing them to cool.Motorized Pressure Method.—In the pressure method, the tip is used to apply heat to a pin formelting a sweat joint. The air pressure is forced through the hole to melt sweat joints without contacting3-18
the delicate pad. This method is seldom used because it is not effective in preventing sweating of the leadto the hole nor for cooling the workpiece.Hot-Air Jet Method.—The hot-air jet method uses pressure-controlled, heated air to transfer heat tothe solder joint without physical contact from a solder iron. This permits the reflow of delicate jointswhile minimizing mechanical damage.When the solder is removed from the lead and pad area, the technician can observe the actualcondition of the lead contact to the pad area and the amount of the remaining solder joint. From theseobserved conditions, the technician can then determine a method of removing the component and lead.With straight-through terminations, the component and lead may be lifted gently from uncoatedboards with pliers or tweezers. Working with clinched leads on uncoated boards requires that all sweatjoints be removed and that the leads be unclinched before removal.The techniques that have been described represent the successful methods of desolderingcomponents. As mentioned at the beginning of this section, the 2M technician must decide which methodis best suited for the type of solder joint. Two commonly used but unacceptable methods of solderremoval are heat-and-shake and heat-and-pull methods.In the heat-and-shake method, the solder joint is melted and then the molten solder is shaken fromthe connection. In some cases, the shaking action may include striking the assembly against a surface toshake the molten solder out of the joint. This method should NEVER be used because all the solder maynot be removed and the solder may splatter over other areas of the board. In addition, striking the boardagainst a surface can lead to broken boards, damaged components, and lifted pads or conductors.The heat-and-pull method uses a soldering iron or gang-heater blocks to melt individual or multiplesolder joints. The component leads are pulled when the solder is melted. This method has manyshortcomings because of potential damage and should NOT be attempted. Heating blocks are patterned tosuit specific configurations; but when used on multiple-lead connections, the joints may not be uniformlyheated. Uneven heating results in plated-through hole damage, pad delamination, or blistering. Damagecan also result when lead terminations are pulled through the board.When desoldering is complete, the workpiece must undergo a careful physical inspection for damageto the circuit board and the remaining components. The technician should also check the board forscorching or charring caused by component failure. Sometimes MEASLING is present. Measling is theappearance of light-colored spots. It is caused by small areas of fiberglass strands that have been damagedby epoxy overcuring, heat, abrasion, or internal moisture. No cracks or breaks should be visible in theboard material. None of the remaining components should be cracked, broken, or show signs ofoverheating. The solder joints should be of good quality and not covered by loose or splattered solder,which may cause shorts. The technician should examine the board for nicked, cracked, lifted, ordelaminated conductors and lifted or delaminated pads.Q10. When does most printed circuit board damage occur?Q11. What procedure involves the use of finely braided copper wire to remove solder?Q12. What is the most effective method of solder removal?Q13. When, if at all, should the heat-and-shake or the heat-and-pull methods of solder removal beused?3-19
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NONRESIDENTTRAININGCOURSESEPTEMBER
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PREFACEBy enrolling in this self-st
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TABLE OF CONTENTSCHAPTERPAGE1. Micr
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Module 11, Microwave Principles, ex
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INSTRUCTIONS FOR TAKING THE COURSEA
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THIS PAGE LEFT BLANK INTENTIONALLY.
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CHAPTER 1MICROELECTRONICSLEARNING O
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VACUUM-TUBE EQUIPMENTVacuum tubes w
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SOLID-STATE DEVICESNow would be a g
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FILM INTEGRATED CIRCUITS are broken
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Development of a microelectronic de
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Figure 1-9.—Crystal furnace.The c
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Figure 1-12.—Planar-diffused tran
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Figure 1-14.—Vacuum evaporation o
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Figure 1-17.—Cathode-sputtering m
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Q23. How do the two types of monoli
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Figure 1-21A.—TO-5 mounting PLUG-
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Dual Inline PackageThe dual inline
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wafer, as shown in figure 1-27. Thi
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Figure 1-29.—J-K flip-flop discre
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Figure 1-31.—Lead numbering for a
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Figure 1-34.—Manufacturer's Data
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comparison to the distance between
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LEVEL III.—Drawers or pull-out ch
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Conductors located several layers b
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Figure 1-43A.—Evolution of modula
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ENVIRONMENTAL CONSIDERATIONSThe env
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SUMMARYThis topic has presented inf
Page 60 and 61: Rapid development has resulted in i
Page 62 and 63: Large DIPs are being used to packag
Page 64 and 65: MINIATURE ELECTRONICS are card asse
Page 66 and 67: Three methods of interconnecting ci
Page 68 and 69: ANSWERS TO QUESTIONS Q1. THROUGH Q5
Page 70 and 71: A43. Conventional printed circuit b
Page 72 and 73: Upon satisfactory completion of a 2
Page 74 and 75: One such improvement in system test
Page 76 and 77: those that should be observed when
Page 78 and 79: Figure 2-2.—Low voltage Handpiece
Page 80 and 81: Figure 2-6.—Rotary-drive machine
Page 82 and 83: Figure 2-9.—Pana Vise.HAND TOOLSF
Page 84 and 85: Figure 2-10a.—Pliers.TweezersView
Page 86 and 87: Even though all the items are not u
Page 88 and 89: Figure 2-14.—Stereoscopic zoom mi
Page 90 and 91: other than eutectic, go through a p
Page 92 and 93: A1. Chief of Naval Operations (CNO)
Page 94 and 95: CAUTIONTHIS SECTION IS NOT, IN ANY
Page 96 and 97: The coating material can best be id
Page 98 and 99: Figure 3-3.—Rotary tool conformal
Page 100 and 101: Figure 3-4A.—Eyelets (interfacial
Page 102 and 103: Figure 3-5B.—Clinched leads. SEMI
Page 104 and 105: Figure 3-8A.—Terminals. PIN AND T
Page 106 and 107: Figure 3-8E.—Terminals. SOLDER CU
Page 108 and 109: Figure 3-10.—Solder wicking.This
Page 112 and 113: INSTALLATION AND SOLDERING OF PRINT
Page 114 and 115: Figure 3-15.—Component arrangemen
Page 116 and 117: Figure 3-16.—Thermal shunt.APPLIC
Page 118 and 119: Removal of Plug-In DIPsTo remove pl
Page 120 and 121: Figure 3-19.—TO mounting techniqu
Page 122 and 123: Figure 3-21.—Flat pack in protect
Page 124 and 125: Figure 3-23.—Pcb conductor damage
Page 126 and 127: REPAIRING DELAMINATED CONDUCTORS.
Page 128 and 129: 5. The repair is completed using th
Page 130 and 131: SAFETYSafety is a subject of utmost
Page 132 and 133: OBJECT OR PROCESSWORK SURFACESFLOOR
Page 134 and 135: 8. When moving an ESDS device or as
Page 136 and 137: Power ToolsHazards associated with
Page 138 and 139: dispensers will prevent many accide
Page 140 and 141: A GOOD SOLDER JOINT is bright and s
Page 142 and 143: ANSWERS TO QUESTIONS Q1. THROUGH Q3
Page 145 and 146: APPENDIX IGLOSSARYALLOWANCE PARTS L
Page 147 and 148: MODULAR PACKAGING—Circuit assembl
Page 149: APPENDIX IIREFERENCE LISTCHAPTER ON
Page 152 and 153: Microelectronics—Continuedpackagi
Page 155: Assignment QuestionsInformation: Th
Page 158 and 159: 1-7. Which of the following charact
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1-24. Vacuum evaporation and cathod
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___________________________________
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1-49. Ground planes and shielding a
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1-65. Which of the following types
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ASSIGNMENT 2Textbook assignment: Ch
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2-20. Turret, fork, and hook termin
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2-39. Component leads may be clippe
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2-52. To ensure a good mechanical b
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