Adjustment of PCB assembly wave soldering technicsfactors

What are the adjustments factors to the SMA wave soldering technics in the PCB manufacturing factory? The PCB assembly workshop technicians share the following factors.

(1) Coating of flux. In the PCB assembly wave soldering, the uneven coating on the surface of the PCB on which the SMC/SMD has been mounted increases the difficulty in uniform coating of the flux.It’san effective way to overcome the spray shadow effectby keeping the spray head's spray direction perpendicular to the PCB surface.

(2)Pre-heat temperature. In PCB assembly wave soldering, the preheating temperature must take into account not only the activation temperature required by the flux, but also the preheating temperature required by the SMC/SMD itself. Generally, the preheating temperature selection principle: the difference between the temperature of the SMA after passing through the preheating zone and the temperature of the solder peak is about ≤100 °C.

(3)Solder, soldering temperature and time. Since SMA is immersed wave soldering, the solder in the soldertankis much morecontaminatedduring working than the THT wave soldering, so pay special attention to monitoring the solder content of the solder tank. The principle of selecting the highest temperature and soldering time for PCB assembly wave soldering is that in addition to providing heat to the weld, heat must be supplied to heat the components to reach the soldering temperature. When higher preheating temperature is used, the temperature of the soldertankcan be appropriately lowered, and the soldering time can be extended as appropriate. For example, at 250 ° C, the sum of the longest immersion time of a single peak or the total immersion time of a double peak is about 5 s, but at 230 ° C, the longest time can be extended to 7.5 s.

(4) PCB pinch speed and angle. In PCB assembly wave soldering, the better angle is about 6 ° ~ 8 °, and the wave soldering surface of SMA is generally not as flat as the peak soldering surface of THT, which is a potential factor leading to tipping, bridging connection and leakage welding. Therefore, the pinch angle of the PCB assembly wave soldering should be slightly larger, generally between 6 ° and 8 °. The pinch speed must be selected to make the second peak has sufficient immersion time so that larger components can absorb enough heat to achieve the desired soldering effect.

(5) Immersion depth. The immersion depth refers to the depth of the PCB immersed in the wave solder in the SMA wave soldering. The depth of the first peak is deeper to obtain a larger pressure to overcome the shadow effect, and the time through the nozzle is shorter, which is beneficial to the remaining flux is enough dose available for the second peak to use.

(6) Cooling. In PCB assembly wave soldering, slow cooling is used for more than 2 minutes after soldering, whichhas great significance in reducingstress caused by temperature drastic changes and avoidingcomponent damage.