Reasons and solutions for defects in reflow soldering and wave soldering

There are several different methods for reflow soldering, including wave soldering and gas-phase reflow soldering. Wave soldering is the process of moving a PCB through a solder wave to cover the solder pads on the PCB, and then placing the mounted components onto the solder. Gas phase reflow soldering involves placing the PCB and mounting components in a heated furnace to melt the solder and solder the components onto the PCB. This article has collected and organized some materials, hoping to have significant reference value for readers.

1、 Non wetting of solder joints/poor wetting

Usually, poor wetting refers to the inability of the solder alloy to spread out well, resulting in poor solder joints and directly affecting their reliability.

Cause of occurrence:

1. The coating on the surface of the solder pad or pin is oxidized, and the presence of the oxide layer blocks the contact between the solder and the coating;

2. Insufficient coating thickness or poor processing can easily cause damage during assembly;

3. Insufficient welding temperature. Compared to SnPb, commonly used lead-free solder alloys have a higher melting point and significantly lower wettability, requiring higher welding temperatures to ensure welding quality;

4. If the preheating temperature is too low or the activity of the flux is insufficient, the flux cannot effectively remove the oxide film on the surface of the solder pads and pins;

5. Another issue is the mismatch between the coating and solder, which may lead to poor wetting;

6. With the increasing adoption of 0201 and 01005 components, the amount of solder paste printed is small, and the flux in the solder paste quickly evaporates under the original temperature curve, which affects the wetting performance of the solder paste;

7. The solder or flux is contaminated.

Preventive measures:

1. Store boards and components as required, and do not use deteriorated welding materials;

2. Select plates with coating quality that meets the requirements. Generally speaking, it requires at least 5 μ M-thick coating to ensure that the material does not expire within 12 months;

3. Before welding, the brass pins should be coated with a layer of 1-3 first μ The coating of m, otherwise the Zn in brass will affect the welding quality;

4. Reasonably set process parameters, increase preheating or welding temperature appropriately, and ensure sufficient welding time;

5. The wetting behavior of various solder joints in nitrogen protection environment can be significantly improved;

6. When welding components 0201 and 01005, adjust the original process parameters to slow down the creep slope of the preheating curve, and make adjustments in solder paste printing.

2、 Bridging defect

1) Reasons for the formation of bridging defects

(1) The PCB board design is unreasonable, and the pad spacing is too narrow;

(2) Excessive impurities in solder hinder the detachment of solder;

(3) The preheating temperature of PCB is low, and the viscosity of melted solder is high, making it difficult to detach from the pins;

(4) If the welding temperature is too low or the speed of passing through the plate is too fast, the viscosity of the melted solder is high and it is not easy to fall off the pins;

(5) Insufficient flux or poor activity.

2) Solution to bridging defects

(1) Design according to PCB design specifications, reflow soldering can be used for smaller pad spacing;

(2) Regularly check whether impurities in solder exceed the standard and remove slag;

(3) Set a reasonable preheating temperature;

(4) Adjust welding temperature and plate passing speed;

(5) Reasonably use qualified soldering flux.

3、 Sharpening defect

1) Reasons for the formation of pointed defects

(1) The temperature of the tin pot is low, and the solder cools quickly;

(2) If the welding temperature is too low or the speed of passing through the plate is too fast, the viscosity of the melted solder is high and it is not easy to fall off the pins;

(3) The electromagnetic pump peak welding machine has a high peak height or the pins of the components are too long, making the bottom of the pins unable to contact the peak;

(4) Insufficient flux or poor activity.

2) Solution to Sharpening Defects

(1) Adjust the temperature of the tin pot;

(2) Adjust welding temperature and plate passing speed;

(3) Control the peak height of the wave;

(4) Reasonably use qualified soldering flux.

4、 Leakage welding, virtual welding, wetting

1) Reasons for defects such as missed soldering, virtual soldering, and poor wetting

(1) Oxidation or contamination of component pins, pads, and PCB pads;

(2) The metal electrode at the end of the chip component does not have good adhesion or uses a single-layer electrode, resulting in cap detachment during welding;

(3) The design of PCB is unreasonable, which can produce shadow effects and cause welding defects such as solder leakage;

(4) PCB warping, poor contact between the raised position and the wave peak;

(5) The two sides of the conveyor belt are not parallel;

(6) Insufficient activity of flux, resulting in poor wetting;

(7) The preheating temperature of the PCB is too high, causing the flux to become inactive and resulting in poor wetting.

2) Solution to defects such as missed soldering, virtual soldering, and poor wetting

(1) Pay attention to the storage environment of components and PCBs;

(2) Surface mount components with a three-layer end structure should be selected;

(3) The layout and arrangement direction of components should follow: smaller components should be placed in front, and shading effects should be avoided as much as possible due to mutual occlusion;

(4) The warpage of PCB board is less than 0.8% -1.0%;

(5) Horizontal conveyor belt or conveyor frame;

(6) Use qualified soldering flux;

(7) Set the appropriate preheating temperature.

The above is the relevant content on the causes and solutions of defects in reflow soldering and wave soldering compiled by Chuangxin Testing. We hope it will be helpful to you. Chuangxin Testing is a professional testing institution for electronic components, currently mainly providing integrated circuit testing services such as capacitors, resistors, connectors, MCU, CPLD, FPGA, DSP, etc. Specializing in functional testing of electronic components, appearance testing of incoming electronic components, anatomical testing of electronic components, acetone testing, X-ray scanning testing of electronic components, and ROHS component analysis testing. Welcome to call, we will be happy to serve you!