One step in the PCB assembly process is applying solder paste to the boards. Deposition is either integrated into the pick-and-place machine or done with stand-alone equipment. The paste is deposited in specific locations and amounts as guided by a stencil so that the board can then be populated with components like resistors, capacitors, application-specific integrated circuits (i.e. AISCs or chips), and EMI shields.
If components are placed incorrectly, the circuit may not function reliably or as intended. What’s more, if the solder paste is not located correctly, it becomes difficult or impossible to solder the components in the right places. Improper solder paste deposition can prevent components from being fully secured to the board.
At Circuit Pak, we provide optical solder paste inspection (SPI) as part of our PCB assembly services. Keep reading to learn what it is, why it’s important, and how it works.
What Is Solder Paste Inspection (SPI)?
SPI is the process of verifying that solder paste has been applied correctly to a PCB. Carefully prepared stencils are used to align and apply the paste; however, there is always a chance for error. Inspection can catch these errors early in the assembly process so they can be corrected before an entire batch is affected.
SPI checks these things:
- Presence or absence of solder in specific locations
- Deposit dimensions: height, volume, surface area
- Composition of paste
- Placement
- Stencil offsets
- Surface defects
The machine uses optical technology to measure the solder paste deposits, sensing the height, width, and layout of each solder line. If the detected solder paste is within parameters, the PCB passes inspection and continues through assembly. If not, the point(s) of failure are identified so the deposition process can be adjusted.
Benefits of Solder Paste Inspection (SPI)
SPI catches errors before they affect soldered components and the entire batch of PCBs. It has several benefits in the PCB assembly process:
- Defect Prevention. It is always preferable to identify and resolve problems as early as possible to avoid scrap or rework later. SPI finds places where solder paste was applied incorrectly or not at all so they can be corrected. This may involve refining the stencil, adjusting paste composition, part alignment, or other changes.
- Reliability. SPI is a positive identification process, so in addition to identifying problems, it also verifies when solder paste is applied correctly. This acts as a “green-light” for further assembly and minimizes the risk of disruptions to production.
- Cost-Effective Operations. Finding and fixing errors and keeping defective PCBs out of the assembly line results in less waste, less time spent reworking components, and less money for supplies and labor.
How Does Solder Paste Inspection (SPI) Work?
SPI inspection uses 3D imaging software and computer algorithms to compare the PCB being inspected to accurate reference images and data. In this way, it can detect inconsistencies in soldering paste, unexpected or missing placement of paste, and incorrect dimensions of paste deposits. SPI tools can also detect physical damage, scratches, and stains on the PCB surface.
Industry 4.0 and SPI
SPI technology is continually improving. AI and machine learning tools can detect minute variations in paste deposits in even highly complex PCB layouts. As optics technology advances, scans become more accurate and make it easier to identify problems, troubleshoot, and resolve them quickly.
Industry 4.0 makes it possible to connect all the machines in an assembly line and computers with inspection and diagnostic software in a secure network. This creates an efficient feedback loop to find and define specific problems, and then make adjustments at the point of need in nearly real-time.
Choose Solder Paste Inspection Services From Circuit Pak
At Circuit Pak, we’re committed to quality at every point of the PCB assembly process. With SPI services, we help ensure finished PCBs are built correctly and function reliably and as intended. Contact us to learn more about our PCB assembly services, or to request a quote.