If you’ve come across the words Type 4, Type 5, or T4, T5, T6 regarding 焊锡膏 and wondered what that meant, you’ve come to the right place.
First, note that while 焊锡膏 might look like a uniform gray blob, it’s actually a carefully engineered mixture of powdered metal and a gooey medium called flux. The powder gives solder paste its structure and functionality, while the flux enables it to flow and adhere to components during reflow.
When someone talks about “Type 4 solder paste” or “T4 paste,” they’re referring to the size of those powdered metal particles within the paste
In this article, we describe what the different powder sizes are and why we have these different powder sizes in the first place.
An Overview of Relative Sizes
When you zoom in microscopically, the powder takes the form of tiny spheres. For each powder size or type, there is a minimum and maximum sphere size which defines it. These sphere sizes are measured in micrometers, where 1 micrometer (µm) = 0.000001 meters. The table below shows the minimum and maximum sphere size for each powder type and gives a sense of the relative sizes of these spheres.
Solder paste or powder is classified on a scale that ranges from Type 1 (largest) to Type 10 (smallest). This is perhaps counterintuitive at first since 10 is a larger number than 1, but if we started at 10 and wanted to make smaller and smaller particles, we couldn’t keep going after getting down to 1. In contrast, we can, in the future, keep going up in number – Type 11, Type 12, etc.—though those types don’t really exist yet.
For reference, Type 1 powder, which ranges from 75-150 µm, is about the same diameter as a human hair. Type 10 powder, which ranges from 1-3 µm, is about the size as a bacterium or cell organelle.
Why Does Powder Size Matter?
The size of the powder particles impacts how solder paste performs in real-world applications. Smaller particles allow solder paste to flow through finer stencil apertures, which is essential as components and PCBs get smaller. But finer particles also have trade-offs, like being more prone to oxidation and requiring stricter process controls.
The electronics industry’s needs are always changing, and so are its standards. Not long ago, Type 3 solder paste (particle size: 25-45 µm) was the norm. It worked well for larger components like 0805s and 0603s.
As components got smaller and tighter, Type 4 (20-38 µm) became the go-to standard, supporting finer pitches like 0201s and 0.5mm BGAs. Today, Type 4 dominates most SMT assembly lines.
But miniaturization isn’t slowing down. Now, we’re seeing a shift toward Type 5 (15-25 µm) and even finer powders like Type 6 (5-15 µm) for cutting-edge technologies such as microLEDs, chip-scale packages, and advanced system-in-package (SiP) designs.
How to Choose the Right Powder Size
Here’s a rule of thumb: Stick with the largest powder size your application allows. Smaller powders offer precision but come with trade-offs like higher cost and tighter process requirements.
To guide your decision, consider:
- The 5-Ball Rule: The smallest stencil aperture should be at least five times the diameter of the largest powder particle. For example, Type 4 can handle apertures down to ~190 µm, while Type 5 can manage ~125 µm.
- Your Components: If you’re working with 0201s or 0.5mm BGAs, Type 4 is usually sufficient. For 01005s or ultra-fine pitch components, Type 5 or finer may be required.
- Your Equipment: Printing and reflow processes may need adjustments for finer powders, such as reducing squeegee pressure or optimizing reflow atmospheres.
For more detailed information, you might also want to read our technical paper Solder Paste Powder: When to Downsize.
最终想法
As electronics continue to shrink, solder paste powder size is becoming more important than ever. Understanding what size you need – and why – can help you avoid production issues and ensure reliable assembly outcomes.
At AIM Solder, we’ve been making and perfecting solder powders for decades, offering a full range from Type 3 to Type 7 and beyond. Whether you’re sticking with the industry-standard Type 4 or stepping up to finer powders, we’re here to help you make the right choice for your manufacturing needs.
Understanding solder paste powder size might seem like a small detail, but in the world of electronics, those details make all the difference. Have more questions? Drop us a line – we’re here to help you solder smarter, not harder!
