After reflow soldering, solder joints turn black, which is mainly related to flux residues in the solder paste. By controlling solder paste usage, optimizing reflow soldering parameters, and strengthening the cleaning process, residue problems can be effectively reduced and soldering quality can be improved.

The solder paste scrapping standards cover key indicators during use, such as viscosity changes, contamination status, and opening time. In practice, if obvious deterioration or contamination occurs, it must be discarded immediately to ensure welding quality.

The tombstoning issue in QFN packages is often caused by improper solder paste selection or insufficient process control. Correctly selecting solder paste and optimizing process parameters can effectively reduce such defects and improve product yield.

No abnormalities were found in the stencil aperture, yet solder paste printing still exhibits insufficient solder deposition. The core issue may lie in the solder paste itself or the operating process. This article analyzes common causes and provides practical recommendations to help resolve the challenge of insufficient solder deposition during solder paste printing.

The shelf life of solder paste after opening is generally 1 to 3 months, depending on environmental conditions. The shelf life of solder paste is directly related to soldering quality and production efficiency, and using it beyond the expiration date may lead to adverse consequences. Proper storage and management of solder paste are key links in the SMT process.

Improper storage temperature of solder paste will directly affect its performance, leading to reduced soldering quality. Properly controlling the storage conditions of solder paste is key to ensuring stable production.

Solder paste clumping is a common problem in SMT production, which directly affects soldering quality. Focusing on the phenomenon of solder paste clumping, this paper analyzes its causes and provides practical solutions and prevention key points to help engineers respond quickly.

Moisture absorption of solder paste can lead to defects such as bubbles and voids during reflow soldering, affecting solder quality. Proper storage and use of solder paste are critical.

The viscosity of solder paste fluctuates sharply, directly affecting soldering quality and production efficiency. By observing the condition of the solder paste, using testing tools, and applying adjustment methods, problems can be quickly identified and resolved to ensure process stability.

Poor Wetting of Lead-Free Solder Paste: Is It a Solder Paste Issue or a Process Issue? Through practical case analysis, this article explores the common causes of poor wettability of lead-free solder paste and corresponding countermeasures, providing practical reference for SMT processes.

Inadequate solder paste warm-up will affect SMT soldering quality and lead to various defects. This paper analyzes actual cases and summarizes common problems and solutions.

In the solder paste printing process, excessively long residence time of solder paste can cause various problems, such as reduced tackiness, slump, and poor soldering. Timely control of solder paste usage time is key to ensuring product quality.

QFN soldering places extremely high demands on the activity, particle size distribution and metal content of solder paste. It is recommended to use Type 4 or Type 5 rosin-based no-clean solder paste with a metal content of 90.5±0.3%. In actual production lines, improper solder paste selection or mismatched printing parameters can easily lead to typical defects such as solder bridging, open soldering, tombstoning and bottom bridging.

Solder paste begins to deteriorate rapidly after being exposed to room temperature for more than 4 hours. This deterioration is significantly accelerated when ambient humidity exceeds 60%RH or temperature exceeds 25℃, as viscosity increases, metal particle settling and flux delamination become markedly more severe, directly impacting the shelf life of the solder paste and printing yield. Production lines must strictly control the time window between taking the solder paste out of cold storage and putting it into use on the machine.

Low-temperature solder wire is suitable for soldering heat-sensitive components such as MLCCs, tantalum capacitors, LED beads, CMOS image sensors, and flexible FPCs. Its 138℃ melting point significantly reduces the risk of thermal shock. Combined with the moderately active rosin core and low residue, it balances wettability and component reliability in both SMT reflow and manual touch-up soldering.

Dull solder joints after solder paste soldering are often not caused by a single factor, but rather the combined effect of multiple process variables such as insufficient solder paste activity, mismatched reflow temperature profile, unreasonable stencil aperture design, low nitrogen purity, or oxidation of PCB pads. Among these, the metal content of the solder paste itself and the flux system have the most direct impact on the final solder joint gloss.

Low-temperature solder paste is suitable for heat-sensitive components such as MLCCs, LED beads, flexible printed circuits, and connectors with plastic housings. Its melting point is typically 138°C to 170°C, more than 50°C lower than that of traditional solder paste, which can significantly reduce the risk of thermal stress damage, while imposing higher requirements for reflow soldering zone settings and nitrogen protection.

In manual soldering, the selection of solder wire diameter directly affects drag soldering efficiency and solder joint formation quality. Thick solder wire is suitable for large-area pads and quick solder replenishment but is prone to causing bridging, while thin solder wire facilitates precise pin control but imposes higher requirements on operation rhythm. Actual production lines need to comprehensively weigh factors based on PCB pad size, component spacing, and operation takt time.

The voids in solder joints formed by bar solder wave soldering are closely related to the material properties of the solder bar. Excessive impurity elements such as arsenic and antimony in high-purity lead-free solder bars will significantly aggravate void formation, while an imbalanced tin-copper alloy ratio or fluctuations in silver content directly affect the surface tension and wetting behavior in the molten state, thereby altering the gas escape paths inside the solder joint.

The occurrence of solder balling during the reflow soldering process is not necessarily a quality issue with the solder paste itself; it is more often related to the coupling of multiple factors such as printing parameters, stencil design, temperature zone settings, and ambient humidity. Especially when the solder paste is unevenly heated during the reflow stage or the solvent volatilizes insufficiently, splashing-type solder balls are highly likely to be induced. Therefore, troubleshooting should start from the storage conditions of the solder paste, the matching of the reflow soldering profile, and the coordination of the PCB pad layout.