The wave soldering process is a complex process of the interaction between the surface of the welded metal, molten solder and air. The quality of wave soldering is related to the process parameters and equipment conditions of the printed board, components, solder, flux, soldering temperature and time, etc. Many factors are related. In the production process, according to the specific conditions of the unit’s equipment and products, by selecting the appropriate solder and flux, adjusting the process parameters, constantly summing up experience, and strengthening the daily maintenance of the equipment, so that the equipment is always in good condition, and strive for peaks. The defective welding rate is reduced to a minimum. Guangshengde Technology will share with you the analysis and preventive measures of common welding defects in wave soldering.

Wave soldering work video

1. Insufficient wave solder

Insufficient wave solder means that the solder joints are dry and the solder joints are incomplete and not full. The solder filling height in the insertion holes and vias is less than 75%, mostly caused by semi-wetting. Preventive measures: the preheating temperature is controlled at 90～130℃, the upper limit of the complex board; the tin wave temperature is controlled at (250±5)℃, the welding time is 3～5s; the hole diameter of the insert hole is 0.15～0.4mm larger than the pin diameter ( The thin lead takes the lower limit, and the thick lead takes the upper limit); the wave peak height is generally controlled at 2/3 of the thickness of the printed board; the climbing angle of the printed board is 3°～7°.

2. Too much wave solder (commonly known as package soldering)

Too much wave solder means that the solder ends and pins of the component are surrounded by too much solder, or there are bubbles in the middle of the solder joint, which cannot form a standard meniscus solder joint. Preventive measures: Set the preheating temperature according to the PCB size, whether it is a multilayer board, how many components, and whether there are components to be mounted. The temperature of the PCB bottom surface is 90～130℃. When there are many components to be mounted, the preheating temperature is the upper limit; replace the flux or adjust the appropriate density; improve the quality of the printed board processing, the components are used first, and do not store in a humid environment Medium; when the proportion of tin is less than 61.4%, some pure tin can be added appropriately, and the solder should be replaced when the impurities are too high; the residue should be cleaned up after the work is finished every day.

3. The wave solder joints are bridged or short-circuited (commonly known as continuous tin)

Wave solder joint bridging, also known as connecting bridge, refers to the solder connection between component ends, between adjacent solder joints of components, and solder joints and adjacent wires, vias and other parts that should not be connected electrically. Preventive measures: In addition to the control of preheating temperature, tin wave temperature and welding time, the PCB design must also be reasonable. The long axis of the two ends should be perpendicular to the welding direction, and the long axis should be parallel to the welding direction. Widen the pad of the last pin; the pins of the plug-in components should be shaped according to the hole distance of the printed board and the assembly requirements. ~3mm, the component body is required to be correct when inserting; improve the activity of the flux; remove harmful impurities, reduce the cohesive force of the solder, and facilitate the separation of the solder between the two solder joints.

4, wave solder joints, missed soldering and virtual soldering

Missing soldering and virtual soldering of wave soldering points means that the solder ends of components, pins, or printed board pads are not wetted or partially not wetted. Mostly caused by poor wetting. Precautionary measures: components are used first come first, do not store in a humid environment, and do not exceed the specified use date. The printed board should be cleaned and damp-removed; wave soldering should choose surface mount components with three-layer terminal structure, and the component body and soldering end can withstand the temperature impact of more than two 260℃ wave soldering; SMD layout should be followed The principle of smaller components in the front and avoiding each other as much as possible. Properly extend the length of the remaining pads after lap; the warpage of the printed circuit board is less than 0.8% to 1.0%; adjust the horizontal level of the wave soldering machine and the guide rail or the PCB transmission rack; the large board adopts guide rail support or special tooling for processing; PCB design Time and small components should be arranged as evenly as possible; clean the wave nozzle; use suitable flux.

5. There are solder balls (commonly known as tin balls) on the circuit board after wave soldering

Wave solder balls, also known as solder balls and solder beads, refer to tiny beads of solder scattered around the solder joints. Preventive measures: Strictly inspect the incoming materials, use the components first, do not store in a humid environment, and do not exceed the specified use date. The printed board is cleaned and damp-removed; the matte type solder mask is used; the solder mask is designed to be as far away as possible from the solder joints.

6, wave solder joint pores

Wave solder joint pores refer to the pores and pinholes distributed on the surface or inside of the solder joint. The relatively large blow holes inside the solder joints are also called voids. Preventive measures: Strictly inspect the incoming materials; use suitable solder; the climbing angle of the printed board is 3°～7°; clean the oxide and other residues on the surface of the solder pot before shutting down every day.

7, wave solder joint cold welding and solder joint disturbance

Wave solder joint cold welding, also known as solder joint pattern, refers to the presence of solder disorder traces on the surface of the solder joint. Preventive measures: check whether the motor is faulty; check whether the voltage is stable, handle with care when manually picking and placing the PCB; the tin wave temperature is (250±5) ℃, and the welding time is 3 to 5 seconds. When the temperature is slightly lower, the speed of the conveyor belt is slowed down.

There are some other common problems, such as dirty board surface, mainly due to high solid content of flux, too much coating amount, too high or too low preheating temperature, or due to dirty conveyor belt, oxides and tin dross in the solder pot Caused by too many other reasons. Another example is PCB deformation, which generally occurs on large-size PCBs, mainly due to the large weight of large-size PCBs or unbalanced weight caused by uneven component layout. This requires PCB design to make the components distributed as evenly as possible, and design in the middle of large-size PCBs. Support belt. Another example is the chip drop phenomenon that often occurs when soldering and mounting components. The main reason is that the quality of the patch glue is poor, or because the curing temperature of the patch glue is incorrect, too low or too high will reduce the bonding strength.

During wave soldering, the mounted components fall into the solder pot because they cannot withstand high temperature shock and wave shear force. Some defects that are invisible to the naked eye, such as solder joint grain size, solder joint internal stress, solder joint internal cracks, solder joint brittleness, poor solder joint strength, etc., can only be detected by means of X-ray, solder joint fatigue test, etc. .