What Does SMT Stand for in PCB Manufacturing?

PCB manufacturing has seen multiple technological overhauls over the years. Each one has revolutionized how PCBs can function and gives us the technology we have today. Currently, PCB manufacturing utilizes the SMT process. Now, you might be wondering, “What does SMT stand for in PCB manufacturing?” The simple answer is that it stands for Surface-Mounted technology, but to understand what that means, you will need to dig deeper.

Surface-Mount Technology

SMT is not that easy of a concept to understand. However, as the name implies, the technology works by mounting components onto a blank PCB. the SMT printer can usually do this automatically while taking custom design instructions to build complex PCBs. The reason that this technology is so important is the finesse that it provides. Before SMT, the average PCB could only be so small before it was too difficult to handle. Now, PCB can be much smaller because of the SMT process. This is usually automatic, where previous PCBs were mostly handcrafted, which saves everyone time and money.

SMT Process

The process of SMT starts with feeding the printer the necessary designs for whatever PCB you want to make. The SMT then needs the materials to make the PCB—usually it is soldering paste and the prebuilt components for each unique PCB. The printer then starts to apply the soldering paste to a blank PCB to prepare it for the next step. The SMT printer then starts to function as a PCB component placement machine as it places each separate part onto the paste of the blank PCB. Soon after this step, the PCB is complete and ready for use.

Now that you understand the answer to “What does SMT stand for in PCB manufacturing?” you should be able to make informed decisions about if you want to use SMT.

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Electronics manufacturing using surface-mount technology (SMT) simply means that electronic components are assembled with automated machines that place components on the surface of a board (printed circuit board, PCB). In contrast to conventional through-hole technology (THT) processes, SMT components are placed directly on the surface of a PCB instead of being soldered to a wire lead. When it comes to electronic assembly, SMT is the most frequently used process in the industry.

Electronic assembly encompasses not only placing and soldering components to the PCB, but also the following production steps:

• Applying soldering paste, which is made of tin particles and flux, to the PCB 
• Placing SMT components to the soldering paste on the PCB
• Soldering the boards with a reflow process.

Applying Soldering Paste

Applying soldering paste is one of the first steps in the SMT assembly process. Soldering paste is "printed" on the boards using the silk-screen method. Depending on the design of the board, different stainless-steel stencils for "printing" the paste onto the board and various product-specific pastes are used. Using a laser cut stainless-steel stencil custom made for the project, the soldering paste to be applied only to the areas where components will be soldered. After the soldering paste is on the boards, a 2D-soldering paste inspection is performed to ensure that the paste is evenly and correctly applied. Once the accuracy of the soldering paste application has been confirmed, the boards are transferred to the SMT assembly line, where the components will be soldered.

Component Placement and Assembly

The electronic components to be assembled come in trays or reels, which are then loaded into the SMT machine. During the loading process, intelligent software systems ensure that components are not inadvertently switched or misloaded. The SMT assembly machine then automatically removes each component with a vacuum pipette from its tray or reel and places it on its correct position on the board using precise pre-programmed X-Y coordinates. Our machines are capable of assembling up to 25,000 components per hour. After the SMT assembly is completed, the boards are moved on to the Reflow ovens for soldering, which affixes the components to the board.

Component Soldering

To solder electronic components, we use two different methods, each of which has distinct advantages depending on the order quantity. For series production orders, the Reflow-soldering process is used. During this process, boards are put in a nitrogen atmosphere and are gradually warmed up with heated air until the soldering paste melts and the flux vaporizes, which fuses the components to the PCB. After this stage, the boards are cooled off. As the tin in the soldering paste hardens, the components become permanently affixed to the board and the SMT assembly process is completed.

For prototypes or highly sensitive components, we have a specialized vapor-phase soldering process. In this process, boards are heated until the specific melting point (Galden) of the soldering paste is reached. This allows us to solder at lower temperatures or solder different SMT components at different temperatures depending on their individual soldering temperature profiles.

AOI und Visual Check

Soldering is the second-to-last step of the SMT assembly process. In order to ensure the quality of the assembled boards, or to catch and correct a mistake, AOI visual inspections are performed for almost all series production orders. Using several cameras, the AOI system automatically checks each board and compares the appearance of each board with the correct, pre-defined reference image. If there are any deviations, the operator of the machine is informed of the potential problem, who then corrects the mistake or pulls the board from the machine for further inspection. The AOI visual check ensures consistency and accuracy in the SMT assembly production process.