A thermal processing expert’s take on which tests are ideal for comparisons.

I get asked how I would evaluate the performance of a reflow oven because of my experience with oven testing and participation in the IPC Reflow Oven Process Subcommittee. Some of the questions are basic, such as “Which oven should I purchase?” “Is this new oven as good as the older one?” or “Will it work with my boards or specific process requirements?” Other questions are more complicated: “Will this oven help me produce an acceptable profile with our heavy board?” or “Is this oven better than XYZ’s reflow oven?”

Resolving solder issues requires an examination of the entire process.

The PCB assembly process creates millions of solder joints with great precision, which is why intermittent soldering defects can be particularly frustrating. It is common to assume that soldering materials, such as solder paste and flux, are the primary cause of these issues. But is solder always to blame?

In this article, we explore a real case study and shed light on the importance of accurate diagnosis and vendor collaboration.

Should chemistry formulation and drying time factor into solvent selection?

The practice of periodically wiping excess solder paste off the side of the stencil that contacts the PCB during the printing process can take many different forms and frequencies. The objective of wiping is to remove unwanted solder paste from the contact side of the stencil.

How does solder paste find its way to the contact side of the stencil? By nature, solder paste sticks to both the PCB pad and the stencil. It does not fully release from the aperture upon separation, depending on the area ratio (AR) of the aperture. Very often, transfer efficiency (TE), or the amount of solder paste removed from the aperture, is less than 100%. The remaining paste often forms “strings” that snap back to the stencil’s contact side (Figure 1).

A closer look at mixing methods and automated mixers.

While automation in manufacturing brings efficiency and consistency, the use of automated solder paste mixers is a topic of debate, with significant concerns over their impact on the paste’s properties. This comprehensive analysis delves into why many industry experts advise caution.

Solder paste is not just a blend of materials; it’s a finely tuned compound where each element plays a specific role. The balance between solder powder and flux is crucial, as it determines the paste’s behavior during the printing process and affects the quality and reliability of solder joints. Certain properties of the paste – its viscosity, rheology and thixotropy – fundamentally determine how well it will perform and can be significantly affected by how the paste is handled.