- dissolution of metal oxide on the surface.
U in the welding process, the flux is a liquid, the protective film covering the parent metal and solder surface to prevent its oxygen.
To reduce the surface tension of the tin surface and increase its diffusion.
Welding moment, you can replace the molten state of the solder, the successful completion of the welding.
With the common welding flux for electronics industry
rosin flux
(1) R type (non activated rosin): low activity, mainly used for high requirements of military products.
(2) RmA type (weakly activated rosin): active relaxation, generally used for high reliability electronic products, such as communication products.
(3) Ra type (activated rosin): strong activity, used for general electronic products and more difficult to weld products, residues of corrosive.
water-soluble flux
With strong activity, the residue has a strong corrosive, after welding must be cleaned, mainly for poor welding or assembly of the dense PCB.
Transparent disposable type flux
Residue has no corrosion, no clean, in today's automated assembly line production has greatly improved the productivity and also to avoid the environmental pollution, but the activity of low, so on the PCB and components can be high requirements on welding.
The selection criteria of flux
With the development of electronic industry, electronic assembly is becoming more and more complicated and precise and flux are increased, choose suitable flux very important, engineering personnel flux choice not only to meet the engineering needs, also want to pay attention to the side effects and avoid adverse consequences. The following are key points should be paid attention to the selection of flux.
National regulations or factory custom specifications
Range of use of specific gravity
Effects of operation on the health or environmental pollution of a member
Furnace temperature, preheating temperature and speed of conveyor belt with
Cleaning degree of metal surface
Hand dip, foaming or spray coating PCB
After welding, free of cleaning or need to be cleaned (washed or cleaned with organic solvent)
The flux residue requirements (parts and the welding surface)
The stability of the flux itself
After cleaning whether the white spot
Insulation resistance and corrosion
Storage safety considerations
Solder joints require bright or dull type
Consideration of supplier's ability to supply and after service
Common welding defects and Countermeasures
Factors that produce welding defects
In automatic welding, welding defects of many factors, influence factors of large printed circuit board design, the components can be welding, process parameters of the rationality of equipment intact rate, the quality of solder, flux quality, flux for soldering ability, strict implementation of process documents etc..
Two, the causes of welding defects and Countermeasures reference table
defect
reason
Solving countermeasures
Bubble or pinhole
1, fast welding speed
2, low preheating temperature
3, PCB damp
4, PCB through the hole of organic pollution
1, reduce the transmission speed
2, improve the preheat temperature
3, to ensure PCB dry
4, remove dirt
Bridge (short circuit)
1, poor welding angle
2, solder temperature is low
3, PCB poor solder
4, solder contamination
5, PCB design is bad
6, the flux of fault
7, the surface of the solder oxide
1, adjust the welding angle
2, improve the solder temperature
3, clean the PCB after the wave soldering
4, the replacement of solder
5, modify the PCB design
6, check the quality of flux
7, remove the oxide layer
Tin is not full
1, welding angle is too large
2, solder temperature is too high
1, select the best welding angle
2, reduce the solder temperature
Too much tin
1, welding angle is too small
2, solder temperature is too low
1, choose the best welding corner
2, improve the solder temperature
Solder joint roughness
1, welding temperature is low
2, solder metamorphism
3, the solder is not solidified by vibration
4, before the solidification man-made vibration
1, adjust the furnace temperature
2, the replacement of solder
3, to overcome the impact and vibration of equipment
4, serious technical discipline
icicle
1, high transmission speed
2, solder temperature is low
3, components can be poor
1, reduce the transmission speed
2, increase of tin stove temperature
3, component solderability (scrape, tin)
Substrate deformation
1, tooling fixture failure
2, the operation of the fixture
3, uneven heating of the printed board
4, the welding temperature is too high
5, improper selection of substrate material
1, repair or change the fixture design
2, serious technical discipline
3, repair preheating device
4, adjust the furnace temperature
5, another plate
PCB peel
1, the material quality is poor
2, PCB storage bad
3, solder temperature is too high
1, the replacement of materials
2, strengthen management
3, adjust the solder temperature
The use of flux and precautions
1, flux concentration on the effect of solder effect should by monitoring the proportion to concentration control within the scope of the provisions of the additives.
2, if the proportion is too high, the company should be used to dilute the specified matching diluent to the normal proportion.
3, due to air oxidation, the foaming device of flux should in total hours worked the longest 120 hours of replacing a, rosin content or high production volume customers should be in about 60 hours a replacement.
4, the flux level should at least keep on the foaming stone about an inch, too high is meticulous foam may spill over the PCB board, too low to cause foaming height less than, bubble is too rough, increased consumption of diluent, flux uneven smear, resulting in welding effect is bad.
5, if the use of automatic control, it should be measured once a day to ensure its accuracy. Clean compressed air with a dry, non oil and water free air, and adjust the pressure and flow rate (general pressure set at 5KG/cm2).
6, adjust the angle of the wind blade and the pressure of the wind blade, using the jet angle and the PCB board to move the direction of 10 degrees -15. The assembly angle is too flux blown to the preheater, too small will blow the foam caused poor soldering.