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7 Reasons Why The Surface of SMT Solder Joints on Circuit Boards Appears Sandy

2024-10-14

The Following Reasons May cause the Sandy Feeling on The Surface of SMT Solder Joints:


1. Solder Paste Problem


The metal particles in the solder paste are too large, an inappropriate type is used, or the quality of the solder paste is poor. The solder paste may also absorb moisture when exposed to the air for a long time, making the solder joint surface uneven.

2. Expired Solder Paste


The active agent components of the flux in the solder paste chemically erode the surface of the tin powder, causing "oxides" to form on the surface of the tin powder. This "chemical corrosion" reaction not only changes the melting characteristics of the tin powder but also consumes the active components in the flux, making it difficult to effectively and thoroughly remove the oxides on the surface of the tin powder during reflow soldering. The solder joints where the tin powders are not fully melted will have a dull sandy appearance.

3. Soldering Temperature Is Too High or Too Low


If the soldering temperature is too high, the solder will oxidize quickly, resulting in a rough solder joint surface. If the temperature is too low, the solder will not melt completely, and the solder joint surface will also appear rough.

4. Improper Welding Time


Welding time that is too short or too long will affect the quality of the solder joint. Too short a time may result in the solder not being completely melted, while too long a time may result in solder joint oxidation and welding defects.

Printed Circuit Board Surface of SMT Solder Appears Sandy

5. Poor Atmosphere in The Reflow Oven


If the nitrogen protection in the reflow oven is insufficient or the oxygen content is too high, the solder joint surface may oxidize, resulting in a gritty feel.

6. Contamination of Substrate or Components


Oxide layer, dirt or grease on the substrate surface or component pins may also cause uneven solder joint surface.

7. Improper Cooling Speed


Excessive cooling speed may cause the grain structure of the solder joint surface to be rough, thus showing a sandy feel. It is recommended to control the cooling rate according to the process requirements.


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