1. PCB welding process

 

1.1 introduction of PCB welding process

 

PCB welding process requires manual plug-in, manual welding, repair and inspection.

 

1.2 PCB welding process

 

According to the list of components - plug-in - Welding - cutting foot - Inspection - repair.

 

2. Process requirements for PCB welding

 

2.1 process requirements for component processing

 

2.1.1 before the components are inserted, the solderability of the components must be treated. If the solderability is poor, the pins of the components must be tinned first.

 

2.1.2 after the pin shaping of components, the pin spacing shall be consistent with the corresponding pad hole spacing of PCB.

 

2.1.3 the shape of component pin processing shall be conducive to the heat dissipation during component welding and the mechanical strength after welding.

 

2.2 process requirements for inserting components into PCB

 

2.2.1 the order of inserting components in PCB board is low first and then high, small first and then large, light first and then heavy, easy first and then difficult, general components first and then special components, and the installation of the next process cannot be affected after the installation of the previous process.

 

2.2.2 after the components are inserted, their marks shall be easy to read and read from left to right as far as possible.

 

2.2.3 the polarity of components with polarity shall be installed in strict accordance with the requirements of the drawing, and wrong installation is not allowed.

 

2.2.4 the components on PCB board shall be evenly distributed, neatly and aesthetically arranged, and oblique arrangement, three-dimensional crossing and overlapping arrangement are not allowed; high on one side and low on the other side are not allowed; long on one side and short on the other side are not allowed.

 

2.3pcb board solder joint process requirements

 

2.3.1 the mechanical strength of solder joint shall be sufficient

 

2.3.2 reliable welding to ensure the conductivity

 

2.3.3 the surface of solder joint shall be smooth and clean

 

3. Electrostatic protection during PCB welding

 

3.1 electrostatic protection principle

 

3.1.1 prevent the accumulation of static electricity in the places where static electricity may be generated, and take measures to control it within the safe range.

 

3.1.2 the existing accumulation of static electricity should be eliminated quickly and released immediately.

 

3.2 electrostatic protection methods

 

3.2.1 leakage and grounding. Ground the parts that may or have generated static electricity to provide static electricity release channel. The method of buried line is used to establish "independent" ground wire.

 

3.2.2 elimination of static electricity of non conductor belt: using ion fan to produce positive and negative ions can neutralize static electricity of static power supply.

 

4. Insertion of electronic components

 

The insertion of electronic components should be neat, beautiful and stable. At the same time, it should be convenient for welding and conducive to the heat dissipation of components during welding.

 

4.1 component classification

 

According to the circuit diagram or list, the resistance, capacitance, diode, triode, voltage regulator module, plug-in wire, socket, wire, fastener, etc. are classified.

 

4.2 component pin forming

 

4.2.1 basic requirements for component shaping

 

L the pins of all components shall not be bent from the root, generally more than 1.5mm shall be left.

 

L try to put the component surface with characters in a position easy to observe.

 

4.2.2 pin forming of components

 

Hand processed components shaping, bending pin can use tweezers or small screwdriver to shape the pin.

 

4.3 plug in sequence

 

Manual insertion of components should meet the process requirements. Do not touch the pins of components and the copper foil on the printed circuit board directly.

 

4.4 ways of inserting components

 

Diodes, capacitors, resistors and other components are prone mounted on the printed PCB board.

 

1. Main welding tools

 

Manual welding is a technology that every electronic assembler must master. The correct selection of solder and flux and the selection of welding tools according to the actual situation are the necessary conditions to ensure the welding quality.

 

1.1 solder and flux

 

1.1.1 solder

 

The fusible metal or alloy that can fuse two or more metals and make them a whole is called solder. Among the commonly used tin lead solders, tin accounts for 62.7% and lead 37.3%. The melting point and solidification point of the solder with this ratio are 183 ℃, which can be cooled directly from liquid to solid without semi liquid. The solder joint can solidify rapidly, shorten the welding time and reduce false soldering. The temperature of this point is called eutectic point, and the solder with this composition ratio is called eutectic solder. Eutectic solder has the characteristics of low melting point, consistent melting point and 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.

 

1.1.2 flux

 

Flux is a kind of welding auxiliary material, which has the following functions:

 

L remove the oxide film.

 

L prevent oxidation.

 

L reduce the surface tension.

 

L make the solder joint beautiful.

 

Commonly used fluxes are rosin, rosin alcohol flux, solder paste, zinc chloride flux, ammonium chloride flux, etc.

 

39 tin lead solder wire with rosin flux in the center and 61% tin content is often used in welding, also known as rosin solder wire

 

1.2 selection of welding tools

 

1.2.1 ordinary electric soldering iron

 

The ordinary electric soldering iron is only suitable for the occasions where the welding requirements are not high. Such as welding wire, connecting wire, etc.

 

1.2.2 constant temperature electric soldering iron

 

The important feature of constant temperature electric iron is a constant temperature control device, which makes the welding temperature stable, and is used to weld fine PCB.

 

1.2.3 tin absorber

 

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 tin absorber cavity is discharged; release the lock button of the pressure bar of the tin absorber, and the spring pushes the pressure bar to return to its original position quickly, forming negative air pressure in the tin absorber cavity, which can suck away the molten solder.

 

1.2.4 hot air gun

 

Hot air gun is also known as chip electronic components disassembly and welding platform. It is specially used for welding and disassembly of SMD electronic components (especially multi pin SMD integrated circuits).

 

1.2.5 soldering iron head

 

When the welding pad is large, the cross-section iron head can be selected.

 

As shown in figure-1: when the welding pad is small, the tip type iron head can be selected.

 

As shown in figure-2: when welding multi pin chip IC, knife type soldering head can be selected.

 

As shown in figure-3: when welding the circuit with large changes in the height of components, curved electric soldering iron head can be used.

 

2. Process and method of manual welding

 

2.1 conditions for manual welding

 

L weldable parts must be weldable.

 

L the surface of the metal to be welded shall be kept clean.

 

L use suitable flux.

 

L have proper welding temperature.

 

L suitable welding time

 

2.2 manual welding method

 

2.2.1 holding method of electric soldering iron and solder wire

 

There are three kinds of manual welding methods of holding electric iron: reverse holding, positive holding and pen holding