APTPCB is a PCB manufacturing and PCB assembly factory, focused on delivering stable, repeatable quality for your electronic products. As part of our PCBA Quality & Testing process, we use Solder Paste Inspection (SPI) on the SMT line to control one of the most critical steps in assembly: solder paste printing.

SPI is not a separate service we sell on its own. It is built into our SMT production to help you get higher yields, more reliable joints, and fewer hidden defects from the very first print.

Solder Paste Inspection (SPI) checks how much solder paste has been printed on each pad, and where it has been printed, before any components are placed. On every PCB panel, SPI measures things like paste volume on each pad, paste height and area, offset/misalignment versus pad position, bridging or excessive paste between pads, and insufficient or missing paste in critical areas.

Solder paste printing is often the single biggest source of SMT defects. If it's wrong at the stencil stage, everything afterwards is just 'fixed' on top of a bad foundation.

By catching printing problems immediately, we prevent downstream defects such as open solder joints, bridges and shorts, head-in-pillow defects, and weak or marginal connections.

Using SPI as part of our PCBA process helps you:

For dense, miniaturized, or reliability-focused assemblies, SPI is a key reason your boards pass functional test and survive in the field.

On our SMT lines, Solder Paste Inspection is integrated directly after the solder paste printer and before placement:

This means printing issues are caught immediately at the source, not after components are mounted and reflowed.

Our SPI process is configured around your design and risk level. Typical checks include:

Too little paste can cause opens or weak joints; too much can cause bridging and voids. SPI keeps this under control.

If we detect systematic offset, we adjust printer alignment, stencil cleaning, or pressure.

Data from SPI is used not only to accept/reject boards, but to fine-tune the process.

For modern, high-density PCB assemblies, 3D SPI brings added control:

We use 3D SPI especially on boards with:

For simpler or lower-risk boards, we may use lighter SPI settings aligned with your cost and speed needs.

Because SPI is fully integrated into our PCB assembly process, it directly raises your overall assembly yield. By detecting issues like insufficient, excessive, or misaligned solder paste before components are placed, we prevent many solder-related defects from ever reaching AOI, X-ray, or functional test. That means fewer opens, shorts, and weak joints, as well as significantly less rework and scrap—especially important for fine-pitch, high-density, or BGA-heavy designs where paste volume and position are critical.

SPI also helps stabilize quality over time and across repeat orders. With real-time feedback from the SPI system, we can continuously control and fine-tune the printing process, maintaining consistent results from batch to batch. The inspection data allows us to optimize stencil and pad design, adjust print parameters, and, when useful, share insights with you for future design improvements. The result is more predictable performance, smoother production, and lower risk when you move to smaller packages or more complex layouts.

Solder Paste Inspection is one part of a layered PCBA quality system at APTPCB. Alongside SPI, we also use:

SPI controls solder paste at the start; AOI/X-ray/ICT/FCT confirm solder joints and functionality at the end. Together, they make your PCBAs much more reliable.

Our Solder Paste Inspection is particularly valuable for:

If your design pushes limits on pad size, pitch, or component density, SPI is one of the reasons your boards can still be built consistently and safely.

APTPCB is not just a test provider—we are a PCB manufacturing and PCB assembly factory with SPI, AOI, X-ray, ICT, and Functional Test integrated into our PCBA production lines.

When you place PCB assembly orders with us, Solder Paste Inspection is part of the process, helping us:

If you are planning a new project or migrating an existing design and want a partner that takes PCBA Quality & Testing – including Solder Paste Inspection – seriously, we're ready to help.