Inthe process of PCBA processing, the choice of PCBA tin penetration is also veryimportant. In the through-hole plug-in process, poor tin penetration of PCBboard can easily lead to problems such as solder joint, tin crack and evendropping.
Weshould know these two points about PCBA tin penetration
1<span style=""font-size:14.0pt;font-family:宋體;mso-ascii-font-family:"Times New Roman";">、 Requirements ofPCBA tin penetration
Accordingto IPC standard, the requirement of PCBA tin penetration of through-hole solderjoint is generally more than 75%. That is to say, the standard of solder penetrationof PCBA is no less than 75% of the aperture height (plate thickness) in thevisual inspection of the welded surface, and the penetration of PCBA isappropriate in the range of 75% - 100%. However, when the through-hole isconnected to the heat dissipation layer or the heat conducting layer, more than50% of PCBA tin penetration is required.
2<span style=""font-size:14.0pt;font-family:宋體;mso-ascii-font-family:"Times New Roman";">、 Factors affectingtin permeation of PCBA
Thepoor tin penetration of PCBA is mainly affected by material, wave solderingprocess, flux and manual welding.
Thefactors influencing the tin permeation of PCBA were analyzed
1.Materials
Hightemperature molten tin has a strong permeability, but not all the soldered metals(PCB board, components) can penetrate into, such as aluminum, its surface willgenerally automatically form a dense protective layer, and the internalmolecular structure also makes it difficult for other molecules to penetrate.Second, if there is an oxide layer on the surface of the metal to be welded, itwill also prevent the penetration of molecules. We usually use flux treatment,or gauze brush clean.
2.Wave soldering process
Thepoor tin penetration of PCBA is directly related to the wave soldering process.Re optimize the welding parameters such as wave height, temperature, weldingtime or moving speed. First of all, the rail angle should be properly reduced,and the height of wave crest should be increased to improve the contact amountbetween liquid tin and solder end; then, the temperature of wave solderingshould be increased. Generally speaking, the higher the temperature is, thestronger the permeability of tin is. However, the bearing temperature ofcomponents should be taken into account. Finally, the speed of conveyor beltcan be reduced and preheating and welding time can be increased to make theflux fully remove oxidation The solder joint is wetted and the tin consumptionis increased.
3.Flux
Fluxis also an important factor affecting the poor tin penetration of PCBA. Fluxmainly plays the role of removing surface oxide of PCB and components andpreventing reoxidation during welding process. Poor selection of flux, unevencoating and too little amount of flux will lead to poor tin penetration. Theflux of well-known brand can be selected, the activation and wetting effectwill be higher, which can effectively remove the oxide that is difficult toremove; check the flux nozzle, the damaged nozzle needs to be replaced in time,to ensure that the PCB board surface is coated with appropriate amount of flux,so as to play the soldering effect of flux.
4.Manual welding
Inthe actual plug-in welding quality inspection, a considerable part of theweldments only have the surface solder forming a cone, but there is no tinpenetration in the through hole. In the function test, it is confirmed thatmany of these parts are false soldering, which is more common in the manualplug-in welding, because the soldering iron temperature is not appropriate andthe welding time is too short. Poor tin penetration of PCBA is easy to lead tofalse soldering, which increases the cost of repair. If the requirement of PCBAtin penetration is high and the welding quality is strict, selective wavesoldering can be used, which can effectively reduce the problem of poor solderpenetration of PCBA