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Solder News
Tin beads produced and Prevention
Publisher:  Release time:2011-5-22 
In wave soldering process, the solder ball generation, there are two conditions: one is new to the board to the tin solution, because the water flux or the plate itself, too much or not sufficiently high boiling point solvent evaporation, higher temperatures encountered when suddenly volatile liquid tin, resulting in a larger temperature difference between liquid solder splash out, forming small beading; the other is to leave the liquid solder in the circuit board, when the circuit board with solder wave separation, circuit board extending along the direction of the pin will be pulled out Sok Ju, the role of the flux and solder wetting liquid under the action of their own liquidity, the excess solder will fall back to the tin cylinder, so sometimes the solder splashes falls on the circuit board to form solder beads.
So, we can see, prevention and control in the wave solder ball, we should from the two major aspects, one is the choice of raw materials such as flux On the other hand is the wave soldering process control.

(A), flux in the cause analysis and prevention and control measures
1 , a greater flux of moisture content or excessive, in the pre- Heat failed to sufficiently volatile;
2 , the flux has a high boiling point volatile substances or easy, by not warming up sufficiently volatile;
both because the flux itself Quality problems caused by the actual welding process, you can improve Preheat temperature or slow down the speed of walking board to solve the . In addition, the choice of flux for the former should focus on actual samples provided by the confirmation process, and the standard process when the trial record, in the absence of tin beads happen, the audit supplier provide other descriptive information in the subsequent receipt and acceptance process, suppliers should check the initial descriptive information.

(B), process reasons and preventive control measures
1 , preheat temperature is low, part of the flux is not completely evaporate the solvent; < BR> 2 , take the plate too fast warm-up effect is not reached;
3 , the chain (or PCB board) angle is too small, tin solder liquid surface in contact with the middle of the bubble, the bubble burst resulting solder beads;
4 , the amount of flux coating too large, the excess flux can not flow away or completely without air knife blow the excess flux under;
the emergence of the four bad reasons, and standardization processes are relevant to the determination, in the actual production process, should be strictly in accordance with already good job to set the parameters of the guidance document the correction of the predetermined parameters and can not change the relevant parameters and the technical aspects involved in the following main points:

( 1 ), on the warm-up: General Settings in the 90 -110 degrees C , here by temperature is refers to the warm-up after PCB actual heat plate welding surface temperature, rather than table was Temperature ; If the preheating temperature is mainly the tin is easy to produce weld beads.

( 2 ), on the running board speed: Under normal circumstances, customers are advised to take the board speed set at 1.1 -1.4 m / minutes, but this is not absolute; to go if you want to change the board speed, usually should be to change the preheating temperature for cooperation; example: To take the board faster, so in order to ensure PCB soldering surface preheating temperature can reach a predetermined value, the preheating temperature should be appropriate to improve ; If the preheating temperature change, take the plate too fast, volatile flux may be incomplete, thus resulting in the solder bead welding.

( 3 ), on the chain (or PCB board) of the angle: the angle refers to the chain (or PCB board) and liquid tin plane angle, when PCB tin plate through the liquid surface, should ensure PCB parts liquid surface and the tin is only one plane cut point; not have a large contact surface; when there is no inclination or tilt over an hour, could easily lead tin solder liquid surface in contact with the middle of the bubble, the bubble burst resulting from tin beads.

( 4 ), at peak furnace use, Air Knife The main role is to blow away PCB board excess flux, and to flux in PCB parts surface coating uniformity; Under normal circumstances, air knife angle should 10 degrees; if Air Knife angle adjustment of the irrational will cause PCB flux over the surface, or uneven coating, not only in the warm zone is too easy to drop in the heat pipe, heat pipes affect the life, but also in the immersion tin solution could easily lead to fried tin phenomenon, and the resulting solder ball.

in the actual production, with its own wave of the actual situation, the relevant materials selection, and a strict wave soldering procedures. and in strict accordance with the relevant regulations for production. After experiments show that the strict implementation of the technology under the conditions can be overcome because wave soldering process issues generated tin beads . .

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