Why does PCB pad over wave soldering machine have defects?
Q1: Unreasonable PCB design, too narrow pad spacing.
A: Design according to PCB design specifications.
Q2: The pins of the plug-in component are irregular or the plug-in is skewed, and the pins are close or touching before welding.
A: The pins of the plug-in components shall be formed according to the hole spacing and assembly requirements of the PCB.
Q3: PCB preheating temperature is too low, components and PCB absorb heat during welding, which reduces the actual welding temperature.
A: Set the preheating temperature according to the PCB size, board layer, the number of components, whether there are attached components, etc., and the temperature of the bottom surface of the PCB is between 90 ℃ and 130℃.
Q4: Welding temperature is too low or conveyor belt speed is too fast, so that the viscosity of molten solder is reduced.
A: Tin wave temperature is (250±5) ℃, welding time is 3 ~ 5s. When the temperature is slightly lower, the speed of the conveyor belt should be slowed down.
Q5: Flux activity is poor.
A: Replace the flux
1. The board surface is dirty. This is mainly due to the flux solid content is high, too much coating, preheating temperature is too high or too low, or because the transmission of mechanical claw is too dirty, too much oxide and tin slag in the solder pot and other reasons.
2. PCB deformation. Generally, it occurs on large-size PCB, which is unbalanced due to the large quality of large-size PCB or the uneven layout of components. This requires PCB design to make components as evenly distributed as possible, and design process edge in the middle of large size PCB.
3. Film loss (film loss). Patch adhesive quality is poor, or patch adhesive curing temperature is not correct, curing temperature is too high or too low will reduce the bonding strength, wave soldering can not withstand high temperature impact and wave shear force, so that the attached components fall in the material pot.
4. Other hidden defects. Solder joint grain size, solder joint internal stress, solder joint internal crack, solder joint brittleness, solder joint strength, etc., need X-ray, solder joint fatigue test and other detection. These defects are mainly related to welding materials, adhesion of PCB pads, solderability of component ends or pins and temperature curves.
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