Wednesday, March 9, 2011

【 Weak current College 】 common circuit repair basics "seven" 】

Hardware welding technology
★ Focus
Welding is the maintenance of electronic products are important. Electronic product fault detection out later, immediately is welding.
Welding electronics several heating method: soldering iron, hot air, Tin paste, infrared, laser, etc, many large welding equipment and are based on one or more of combined heating method.
The commonly used welding tools: electric iron, hot-air welding, Tin stove, BGA welding machine
Welding accessories: solder wire, Rosin, suction gun, solder paste, woven wire, etc.
Electric iron is primarily used for welding simulation circuit of discrete components such as resistors, capacitors, inductors, diode, transistor, FET, etc., can also be used for welding size smaller QFP package manifold blocks, of course we can also use it to welding CPU broken pins, you can also supplement to the PCB Board, if the video card or memory of Goldfinger is broken, you can also use soldering repair. Electric iron heating core is actually a lot of laps around the resistance wire, the resistance of length or its selection of materials, power is also different, the ordinary maintenance of electronic products of general use 20W-50W soldering iron. Some top-grade prepare a soldering iron, soldering iron temperature and temperature can be adjusted, internal circuit with automatic temperature control, to maintain constant temperature, the soldering iron is used to better performance, but prices generally more expensive, is more common soldering iron or even dozens of times. Pure Tin melting point is 230 degrees, but we repair solder often contains a certain percentage of lead, resulting in its melting point below 230 degrees, the lowest average is 180 degrees.
New soldering iron first on Tin on Tin, refers to the occurrence of the adhesive on the solder, so that the normal use of a soldering iron, if soldering iron for too long, the surface may vary depending on the temperature is too high and oxidation, oxidation of the soldering iron is a non-stick SN, soldering iron and to pass on Tin treatment for normal use.
Removed, or welding resistance, capacitance, inductance, diode, transistor, FET, in symbol pins on some solder, so you can better make the heat in the past, and so on are all pins can be melted down when or welding. Welded to the attention of higher temperatures, melting rapidly lift the weight, the solder joints smooth, but if the temperature is too high, the deteriorating pads or components.

Complement PCB wiring
PCB Board break situation occurred from time to time, monitor, switching power supply, etc. of the lines thicker, breaking up the line easily, as for the motherboard, video card, the line is very thin notebook, the line spacing is also very little, is going to make up some trouble. To complement these fault lines, first to prepare a very narrow flat mouth scraper, scraper can ability to work with a small screwdriver on the grindstone, make the width of the blade estuary and the width of the PCB wiring. Premium line to the first doctor to PCB break the surface of the insulation blown off, be careful not to push too much so as not to break the line scraping, also note do not put the verges of the PCB wiring on the surface of the insulating scratch-off, to avoid solder adhesion to the verges of the wire surface treatment after going on it evenly coated with a layer of paste, and then use the soldering iron in scratch-off coating line heating coated Tin, then find end-of-mouse, pull out the fine copper wire, single wire coloured paste, and then painted with a soldering iron and solder, soldering iron carefully their copper wire welding the ends of the broken line.
The welding is completed to multimeter test welding of reliability, first to confirm the amount of line ends of the line is connected to, and then also to detect it up line and verges of cord adhesion short circuit.
Plastic soft-line patch
Optical laser headcable, printer, print head line often also fracture phenomena, welding and PCB repair line more or less the same, it is important to note that due to ordinary plastic to withstand very low temperatures, using soldering iron welding temperature to grasp, speed to make faster, avoid plastic is hot bad, moreover, to prevent heat deformation, available small clip the cord clamping position.

CPU broken pins of welding:
CPU broken needle is common, 370 structure of Celeron generation CPU and P4 CPU pin roots firmer, broken needles are generally broken from the Middle, it is easier to weld, as long as the PIN and pads corresponds to place coloured paste, solder after soldering iron heating can be welded on, inconvenience for location specific, using soldering iron, you can use hot air welding machine heating.
Celeron II CPU pins outside too much often uprooted, and pull up on the next following pad is very small, very low success rate for direct soldering and welding fine, needle easily fixed, easily will be touching down, the situation in General has the following several ways: the first way: using the mouse, stripping out of thin copper wire end of one of the root and CPU pad welding together, and then use the line 502 glue sticks to the CPU, the other side of the motherboard CPU holder corresponding pad welding together, from electrical connections between, and patch on the motherboard is no different, a fault is removed from the CPU is convenient. The second way: in the CPU's fault PIN pads on a ball (ball BGA welding can be used with the ball, of course you can also make your own DIY) and then himself for a slightly longer operating point of the needle (, insert the CPU for the break should be housed, and fixed a small piece of cured conductive adhesives (electrically conductive adhesives have a certain degree of flexibility), and then insert the CPU, the CPU block clamp lock so that the CPU might work.
The video card, memory stick, gold finger-jointing:

Video card or memory if repetitious unplug from the motherboard or plug, can cause gold finger falls off, the power supply or ground pins often caused by current is too big to burn out, gold finger to enable them to work properly, it is necessary to fix the Goldfinger, Goldfinger's patch is relatively simple, accessible from the other end of the card using wallpaper scraping down the same knife edge connector, surface clean, 502 glue carefully it alignment in the damaged card, glue solidified later, new knife with wallpaper Glue looks in Goldfinger's scratch-off top of oxides, coloured paste, and then using a fine copper wire it up and break evenTo then.
Manifold of welding:
Without the hot air welding machine, you may consider using a soldering iron with solder to dismantle or welding chips, it is all in chip soldering iron pins are filled with solder and solder with a soldering iron heating loop until all of the PIN solder melting at the same time, you can put the chips were down. The chips down from the Board, you can consider using a thin copper wire from pin down through the chip, and then lift the hand from above.
Hot air welding machine
Hot air welding machine is via hot air heating the solder for welding function, black box inside an air pump, the performance is good air pump noise is small, the air pump is uninterrupted blow out air, air flow along the rubber tube handle, the handle on the front of the inside is the core of heating soldering, will after power up, the air inside the heating down wind mouth out the heat out.
Each soldering station is equipped with more wind, different air nozzle with a different chip to use, in fact, most of the technical staff of only one or two air nozzle can complete most of welding work, that is, the hole of the most widely used. According to our use, hot-air welding machine for general use with the 850 model, its maximum power consumption is usually preceded by 450W, two knob, one is responsiblefor the regulation of wind speed, the other is a regulated temperature. Before you use must be removed from the fuselage at the bottom of the pump screws, otherwise it will cause serious problems. Use, remember to cool the body off the electricity, heating pipe automatically short spurt of trial, in the cooling time, do not pull the power plug to go. Otherwise affect heater life. Note that when the wind in the mouth and 850 spews out hot air temperature is high, the man Burns, do not touch, replace the wind when you want to wait for it to the mouth of the temperature down to action.
The following describes QFP chip replacement
First of all, the power is on, adjust the air flow and temperature control knobs, so that the temperature is maintained at between 250-350 ° c, pull-out is placed in the integrated circuit block, let the nozzle at the desired melting of chip PIN heating and all the pins are melting, can lift the pull-down the chip. Remove the chip, you can paint the right amount of solder pads of the circuit board, with the wind on the mouth heat pads flat as possible, and then in the pads on just the right amount of solder paste, will replace the chip on the Board to align, and then use the wind's mouth to pins evenly blow out the hot, and so all the pins are melting, the welding is completed. Finally, it is necessary to pay attention to check whether the do not short circuit of welding components soldered.

BGA welding:
To use the BAG-on-chip SMD machine, different machines using a method different from that supplied instruction manual with detailed description.
Slots (seat) of the replacement:
Slots (seat) in a larger size, generally used in the production line to welding wave soldering, wave soldering machine can make solder melting into Tin solder paste and mixture formation waves, wave peak and PCB surface contact, making slot (seats) and pad welding together for small batch production or maintenance, often with Tin furnace replacement slot (seats), Tin stove and soldering, are Tin paste to dismantle or welding slot, as long as welding surface and slot (seats) anastomosis.
SMD components of demolition, welding techniques
SMD components of demolition, welding to choose 200 ~ 280 degrees centigrade temperature soldering iron-tipped. SMD resistor, capacitor ceramic substrate of most of the material, this material is easy to break down, so collisions in disassembly, you should master welding control temperature, preheating, touch, and other skills. Temperature is the temperature should be controlled at about 200-250 degrees centigrade. Preheating means will be welded components first 100 ℃ environment preheating 1 ~ 2 minutes, to prevent damage by thermal expansion symbol suddenly. The touch is the actions of the occurrence should PCB solder or imported with heating, try not to touch the component. In addition to control each time the welding time in 3 seconds, after that circuit board welding in ordinary natural cooling. The above methods and techniques apply equally to SMD Crystal diode, triode welding.
SMD integrated circuit PIN number, pitch, small narrow, hardness, if welding temperature properly, it is easy to result pin solder short-circuit, soldered or printed wiring copper foil out of PCB, etc. Demolition of SMD integrated circuit, temperature soldering iron temperature to about 260 ° c, using soldering iron with absorption will IC pin solder all suction, gently with a sharp tip tweezers, side bottom insert IC with a soldering iron heating, gently lift the individually with tweezers IC PIN to enable IC pin gradually and PCB detachment. Zippo lift IC must with the soldering iron heated parts simultaneously to prevent undue haste to circuit board damage.

Swap in a new integrated circuit before leaving the original IC solder all clear, flat cleaning pad. And then will be welded IC PIN using fine sandpaper cleaning, evenly lined Tin, then will be welded IC pin alignment PCB corresponding spot, welding hand light pressure on the surface, prevents the IC IC mobile, another hand dipped in just the right amount of solder soldering operation will IC pin and the corners of the PCB welding fixed again after checking that the integrated circuit model and direction, right after welding, soldering iron temperature adjustment in 250 ℃, a handheld soldering iron to IC pin heating, the other will solder wire sent to heating pin welding, welding heat until all the pins, last check and exclusions pin shorted and soldered, solder joints after cooled with brush dipped in alcohol again clean circuit board and Soldered joints to prevent legacy welding slag.
Maintenance module circuit board failure, should use brush dipped in alcohol cleaning plate PCB, clear the dust and welding slag and other debris, and watch the original circuit board exists soldered short circuits or welding slag, and soon found the point of failure, saving maintenance time.

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