1, PCB welding process
1. 1PCB welding process introduction PCB welding process needs manual plug-in, manual welding, repair and inspection.
1.2PCB welding processes are classified according to the list: components, plug-ins, welding, trimming, inspection and trimming. 2.2 technical requirements. PCB board welding
2. 1 Process requirements for processing parts
2. 1. 1 components must be welded before insertion. If the solderability is poor, the components should be tinned first.
2. 1.2 After pin shaping of components, the pin spacing should be consistent with the corresponding pad hole spacing of PCB.
2. The pin processing shape of1.3 component should be beneficial to heat dissipation during welding and mechanical strength after welding.
2.2 process requirements for inserting components into PCB board
2.2. 1 Components are inserted into PCB in the following order: first low, then high, first small, then big, first light, then heavy, first easy, then difficult, first general components, then special components, and the installation of the previous process cannot affect the installation of the next process.
2.2.2 After the component is inserted, its mark should be easy to read and read from left to right as far as possible.
2.2.3 The polarity of polar components shall be installed in strict accordance with the requirements of drawings, and it is not allowed to be installed by mistake.
2.2.4 Components shall be inserted on PCB evenly and neatly, and diagonal rows, three-dimensional intersections and overlapping arrangements are not allowed; It is not allowed to be high and low; Long pins and short pins are also not allowed.
2.3PCB solder joint process requirements
3.3 electrostatic protection during the period. PCB welding.
3. 1 electrostatic protection principle
3. 1. 1 In places where static electricity may be generated, measures should be taken to prevent static electricity accumulation and control it within a safe range.
3. 1.2 The existing electrostatic accumulation should be eliminated quickly and released immediately.
3.2 electrostatic protection method
3. 2. 1- leakage and grounding. Grounding parts that may or have generated static electricity, and providing static electricity release channels. adopt
The method of burying ground wire establishes "independent" ground wire.
3.2.2 Eliminating non-conductor static electricity: The ion fan generates positive and negative ions, which can neutralize the static electricity of the electrostatic power supply.
4。 The insertion of electronic components requires neatness, beauty and stability. At the same time, it is convenient to weld, which is beneficial to the heat dissipation of components during welding. 4. 1 Classification of components according to circuit diagram or list, resistance, capacitance, diode, triode, transformer, patch cord, socket, conductor and fastener. 4.2 Component Pin Shaping 4.2. 1 Basic Requirements for Component Shaping All component pins shall not be bent from the root, and generally, more than 1.5 mm shall be left ... Try to place the surface of the component with characters in an easy-to-observe position. 4.2.2 Pin shaping of parts Hand-processed parts are shaped, and bent pins can be shaped with tweezers or a small screwdriver.
4.3 Plug-ins shall be manually inserted in sequence and conform to the process requirements. When inserting, do not touch the component pin and the copper foil on the printed circuit board directly with your hands. 4.4 Method of inserting components Diodes, capacitors, resistors and other components are installed on the printed circuit board in a prone position.
5. Welding main tools
Manual welding is a technology that every electronic assembler must master. Correct selection of solder and flux and selection of welding tools according to the actual situation are necessary conditions to ensure welding quality.
5. 1 solder and flux
5. 1. 1 solder
A fusible metal or alloy that can fuse two or more metals into a whole is called solder. Among the common tin-lead solders, tin accounts for 62.7% and lead accounts for 37.3%. The melting point and freezing point of the solder with this ratio are both 65438 083℃, which can be directly cooled from liquid to solid. Without semi-liquid, solder joints can solidify quickly, shorten welding time and reduce virtual welding. This point temperature is called * * * crystal point, and the solder with this composition ratio is called * * * crystal solder. * * * Crystal solder has a low melting point, which is consistent with the freezing point.
Good fluidity, small surface tension, good wettability, high mechanical strength, solder joint can bear large tensile force and shear force, and good conductivity.
5. 1.2 flux
Flux is a welding auxiliary material, and its functions are as follows: ● Remove oxide film.
● Prevent oxidation. ● Reduce the surface tension. ● Make the solder joint beautiful.
Commonly used fluxes include rosin, terpineol flux, solder paste, zinc chloride flux, ammonium chloride flux and so on.
There is rosin flux in the center of 39 Sn-Pb solder wire, with the tin content of 6 1%, which is often used for welding, also known as rosin solder wire.
5.2 Selection of welding tools
5.2. 1 common soldering iron
Ordinary electric soldering iron is only suitable for occasions with low welding requirements. Such as welding wires, connecting wires and the like.
The important feature of constant temperature electric soldering iron is that it has constant temperature control device, which makes the welding temperature stable and is used for welding fine PCB boards.
Tin sucker
The tin absorber is actually a small manual air pump. When the pressure bar of the tin absorber is pressed down, the air in the cavity of the tin absorber is exhausted. Loosen the locking button of the pressure bar of the tin absorber, the spring pushes the pressure bar to return to its original position quickly, and negative air pressure is formed in the cavity of the tin absorber to suck the melted solder away.
Heat Gun
Hot air gun is also called chip electronic component disassembly welding table. It is specially used for soldering and disassembling surface mount electronic components (especially multi-pin SMD integrated circuits).