PCB Manufacturing

SMT Manufacturing Process: Step-by-Step Guide for Electronics Production

SMT manufacturing

We all know that PCBs exist in all electronic products. So PCB fabrication and assembly are very important in all electronics production. Generally, there are two types of technologies majorly used in PCB assembly: SMT (Surface mount technology) and THT (Thru Hole technology). In this article, we will specifically talk about SMT PCB assembly, including the definition of SMT manufacturing and the step-by-step guide for the SMT manufacturing process in electronics production.

What is SMT Manufacturing

SMT means surface mount technology. SMT components are very small size packages like 0201,0402, TSSOP, DFN, QFN, QFP, etc. It’s basically depending on pick and place machine and it’s coding. Pick and place machine having XY coordinates of placement of components. These XY coordinates have many file types like eagle and ASCII, .rpt, etc. Here is the full SMT manufacturing process of the assembly production house generally used. So SMT manufacturing means PCB assembly using surface mount technology, it is one of the most important PCB assembly methods. It is widely used in PCB assembly because of its high accuracy, high efficiency and low cost.

Before the assembly process, the customer sends many files like BOM (Bill of materials), PNP, Gerber, and assembly documents for sourcing, purchasing and DFA to the assembly house. DFA report shows which types of requirements are needed for assembly like BGA inspection, X-Ray, packaging, etc.

SMT PCB Manufacturing

Complete Steps for SMT Manufacturing

After knowing what is SMT manufacturing and its importance in electronics production, we discuss the completed SMT manufacturing process step by step, a total of 16 steps as blow.

  • Create Documents

First of all, the production engineer creates the planning document including BOM files, XY coordinates, and operating instructions.

  • Solder Paste Printing

After that solder stencil was created as per Gerber solder paste. This solder paste has many types like SAC 305, Alpha WS-809, Sn63PB37, Senju M705-LFAC19, etc. These solder materials are basically no-clean and water-soluble. So, it depends on the customer what it wants. After that paste is applied to the PCB.

  • Solder Stencil inspection

In the SMT assembly House, after stencil creation, stencils were visually inspected paste was correctly applied on PCBAs. This inspection checks all paste was correctly deposited on pads to ensure reflow easily. Sometimes, solder bridges in paste layers will be short between pads. So, this inspection is helpful for layout issues also. If any issues are coming in the stencil, so that time it will be caught and reduce rework.

  • Components Placement

Additionally, components are loaded in feeders like reels, tape and reel, and cut tape. Besides this, XY coordinates are loaded in PNP (pick and place) machine for place components. Some PCB designers created XY coordinates with the pin 1 location. So, it’s very helpful for ICs, jacks, and connectors to be placed easily. Components are placed on the PCB with the help of PNP (pick and place) machine. Component placement is critical in the PCB SMT manufacturing process.

  • Quality Checking Before Reflow Soldering

Now, it’s the quality department’s time to check to verify whether all components are placed correctly or not. Because some time components are not placed exactly due to poor solder joints and some layout issues.

  • Reflow Soldering

After that PCBs are gone through the reflow Owen to melt the solder and components are placed easily on its location. This reflow owen has high temperature like 250°C. There are two types of reflow soldering. Pre-reflow and post-reflow. It’s important for quality control. Pre-reflow verifies damage points in PCBs. So that will be easy to solve, avoid rework in future. Pre-reflow will be AOI and Manual inspection. Post reflow is used for very special requirements like for BGAs and LGAs. Post reflows having the flying probe testing.

SMT manufacturing Reflow Soldering

  • AOI Inspection and X-Ray

To add to this, optical inspection is automatic inspection with the help of AOI. This AOI machine has high power with a high-resolution camera to make sure all solder joints are proper or not. This machine reflects the light to the PCB from different angles. AOI machine gives the best resolution in a short time. After that x-ray machines give images, of any defects in PCBs. Sometimes in BGA components solder joints are not properly connected with the inner layer. So, it will be easy for us. X-ray machine provides a very effective solution to detect errors between solder joint connections, misalignments and missing pads for Ball grid arrays. With the help of AOI, we can make sure of part polarity and incorrect placements of components. AOI is one of the most important steps in the SMT manufacturing process.

  • Through-hole Assembly

Through-hole components mean Components having axial leads to install on the PCB. Through-hole components are placed on the PCB after all SMT placement because sometimes it damages other SMT parts when we install them simultaneously. Through-hole assembly provides accuracy with better resolution for soldering. Basically, Through-holes components are installed on PTH holes in order to make contact between layers.

  • ICT (In-Circuit test)

ICT is to be used for Incorrect rotations, value issues and Functionality of components like ICs, resistors, capacitors, etc.

  • Flying Probe test

Basically, the flying Probe test has some probe contacts to ensure continuity test for electrical connection with the help of test points. The flying probe test is most commonly used on assembly Production houses. It’s a very quick and cost-reducing method for very few numbers of circuits. In this testing, first of all test program will be created. It contains a program for probes for testing contacts in PCB with decided voltage and its requirements.

  • Functional Test

Despite this, functional testing is the most important role played in the PCB SMT assembly process. Because this testing fulfils the requirements of PCB designers and assigned voltage, and electric characteristics of PCB. It’s done through functional testing. Functional testing is verifying all PCBAs functions are working correctly. Functional tests are also important in the SMT manufacturing process since only fully functional PCBs are qualified products.

  • PCB Cleaning

PCBAs have irrelevant solder joints available. So, that type are solder needs to be removed to meet requirements of IPC standards. SMT assembly house has various cleaning solvent techniques like solvent-based cleaning, Aqueous cleaning vapour phase cleaning and Etc. Aqueous cleaning is suitable for only water-soluble flux. Other cleaning techniques are cleaning both types of solder flux (No-clean and Water-soluble). Mostly some assembly vendors prefer De-ionized water to remove flux.

  • Conformal Coating

Conformal coating is one type of glue or epoxy type of material applied to PCBs for protection. Conformal coating is applied to PCBs with different techniques like UV coating, a machine-based selective coating method, Dipping and etc. After Conformal coating PCBAs are manually inspected and AOI method. AOI is very easy and fast providing solutions for the proper inspection of PCBAs with the help of Modern technology.

  • Final Quality Check

In this stage, do all inspections and read reports for finished products. Like X-ray reports, functional testing reports, etc. supplied from customer request. All Visual activities are to be done in this stage. If any labels (part number, revision, serial number, date code, etc.), Then labels are to be done at this stage with QC inspection. The SMT manufacturing process is almost finished after this step.

SMT manufacturing Quality Check

  • Packaging and Shipping

Packing boards with proper packing as per customer request (like penalized or de-panelised, QTY in one package). Verify All documents required as per Quality and put all these documents with shipping packages. Most packages are shipped in Bubble wrap, Foam sheets and Paper cushions. Bubble wrap is the most efficient, cost-effective and recyclable method that is majorly used by the SMT assembly House.

Conclusion

SMT manufacturing is widely used in PCB fabrication and electronics production, because of its multiple advantages, such as high efficiency, high accuracy, low cost and high reliability.

Accompanying the development of electronic applications, especially more and more high-density PCBs and electronics devices, SMT manufacturing is more and more important in the electronics industry. This step-by-step guide for the SMT manufacturing process would be helpful to you in understanding SMT PCB assembly.

    Request for Quote