PCB Assembly Services
PCB Assembly Process
What is the PCB Assembly Process?
Now in this era, electronic devices are an essential part of our daily lives. Everything from our mobile phones to our vehicles includes electronic components. At the guts of those electronics is the printed circuit board, also called a PCB. The general public recognizes printed circuit boards once they see them. These are the little green chips covered in lines and copper parts you will find in the guts of gutted electronic devices. A PCB with components mounted on is termed an assembled PCB and also the manufacturing process is named PCB assembly or PCBA for brief. The copper lines on bare board, called traces, electrically link connectors and components to every other. They run signals between these features, allowing the circuit board to function in an exceedingly specifically designed way. These functions range from the straightforward to the complex, and yet the dimensions of PCBs are often smaller than a thumbnail.
PCB Assembly Process Flow
The PCB assembly process may be a simple one, consisting of several automated and manual steps. With each step of the method, a board manufacturer has both manual and automatic options on which to decide. To assist you in better understanding the PCBA process from start to complete, we’ve explained each step intimately below.
Before the PCB Assembly Process
A few preparatory steps should happen before the real PCBA process even begins. This helps printed circuit board manufacturers evaluate the functionality of a PCB structure, and primarily includes a DFM check. Most companies specializing in PCB assembly need the look file of the PCB to begin out, together with the other design notes and specific requirements. This can be therefore the PCB assembly company can check the PCB file for any issues that will affect the PCB’s functionality or manufacturability. This is often a design for manufacturability check, or DFM check, for short.
The DFM check looks at the least the planning specifications of a PCB. Specifically, this inspection examines any misplaced, redundant, or potentially problematic components. Any of those issues may severely and negatively influence the functionality of the ultimate project. for instance, one common PCB design flaw is leaving insufficient spacing between PCB components. This could end in shorts and other malfunctions.
By identifying possible issues before manufacturing starts, DFM reviews can cut manufacturing expenses and stop unexpected expenses. This can be because these checks block the quantity of scrapped boards. As a part of our commitment to quality at a coffee cost, DFM checks come standard with every JHYPCB project order. JHYPCB provides FREE DFM and DFA ask, however, priceless values because Valor DFM/DFA check JHYPCB depends on an automatic system contributing to high speed and accuracies.
Step 1: Applying Solder Paste Using Stencil
First of all, we apply the solder paste to the areas of the PCB board where the components will fit. This can be done by applying solder paste to the stainless-steel stencil. The stencil and also the PCB is held together by a mechanical fixture and so the solder paste is applied by the applicator evenly to any or all openings within the board. The applicator spreads the solder paste equally. So, a correct amount of solder paste must be employed in the applicator. When the applicator is removed the paste will remain within the desired areas of PCB. The grey color solder paste is 96.5% product of tin and contains 3% of silver and 0.5% of copper and it’s lead-free. This solder paste will melt and creates a powerful joint upon application of warmth in step 3.
Learn more about solder paste Inspection.
Solder Paste Printing Using Stencil
Step 2: Automated Placement of Components
The second step in PCB Assembly is the automated placement of SMT components on the PCB board. This can be done by using a pick and place robot. At the planning level, the designer creates a file that may be fed to the automated robot. This file has the preprogrammed X, and Y coordinates of every and each component utilized in PCB, and it identifies the placement of all components. Using this information, the automatic robot will only put the SMD devices on board accurately. The pick and place robots will pick the components from their vacuum grip and place them exactly on top of solder paste.
Before the arrival of robotic pick and place machines, the technician will pick the components using tweezers and place them on PCB by carefully viewing the placement and avoiding any jittering hands. This resulted in a high level of fatigue and eyesight weakness in technicians and resulted in a slowed process of PCB assembly of SMT components. Hence the possibilities of mistakes were high. As the technology matured, automated robots for picking and placing components eased the technician’s work and resulted in fast and accurate components placement. These automatic robots can work 24/7 without tiredness.
Pick and Place Machine
Step 3: Reflow Soldering
The third phase after the parts are placed and solder paste applied is reflow soldering. The reflow soldering is the process where the PCBs together with the components are placed on the conveyor. This belt then moves the PCBs and components in a big oven, which creates a temperature of 250-degree Celsius. These 250 Celsius temperatures are sufficient for the solder to melt. The melted solder will then fix the components upon the PCB and make joints. After the PCB is treated at a hot temperature, it then goes into coolers. These coolers then solidify the solder joints in a controlled fashion. this can create a permanent joint between the SMT component and PCB. Within the case of two-sided PCBs, the PCB side which has fewer or smaller components are going to be treated first from step 1 to three as mentioned above and so comes the opposite side.
Step 4: QC and Inspection
After the reflow soldering, there’s an opportunity that because of some erroneous movement in the PCB holding tray, the components got misaligned and should lead to tangency or open connection. These flaws must be identified and this identification process is termed inspection. Inspection is manual and automatic.
As the PCB has very small SMT components, so visually checking the board for any misalignment or faults may end up in fatigue and eye strains for technicians. So, this method isn’t feasible for advanced SMT boards because of inaccurate results. However, this method is possible for boards having THT components and lesser component density.
For the massive batches of PCB, this method is possible. This method uses an automated machine that has high-powered and high-resolution cameras installed at various angles to look at the solder joints from various directions. The sunshine will reflect the solder joints in numerous angles in step with the standard of solder joints. This automated Optical Inspection (AOI) machine is at an incredibly high speed and takes a very short time to process large batches of PCBs.
The X-ray machine allows the technician to appear through the PCB to work out the inner layer defects. This can be not a typical inspection method and is just employed in complex and advanced PCBs. These review techniques if not correctly used may cause rework or scrap PCB. The inspection needs to be done regular basis to avoid delays, and labor, and material costs.
Step 5: THT Component Fixation and Soldering
The through-hole parts are generally found on many printed circuit boards. These components also are referred to as Plated through holes (PTH). These components have leads that will go through the opening within the PCB. These holes connect with other holes and vias by means of copper traces. When these THT components are inserted and soldered in these holes, then they’re electrically connected to another hole within the same PCB because the circuit is designed. These PCBs may contain some THT components and plenty of SMD components therefore the soldering method as discussed above just in case of SMT components like reflow soldering won’t work on THT components. that the two main sorts of THT components soldering or prototype PCB assembly are
The manual soldering method is that common and typically takes longer than compared to the automated setup for SMT. Usually, one technician is designated to insert one component at a time and therefore the board is passed on to another technician who inserts another component on the identical board. Therefore, the board will move all around the line to induce the PTH components stuffed upon it. This makes the method lengthy and then many PCB designs and manufacturing companies avoid using PTH components in their circuit design. But still, the PTH components are the foremost favorite and customary components for many circuit designers.
- Wave Soldering
During this method, once the PTH components are placed on the PCB, the PCB is placed on the conveyor and is moved to a specialized oven. Here a wave of molten solder is splashed on the PCB bottom layer where the components lead is present. This can solder all the pins without delay. However, this method is just for single-sided PCBs and not for double-sided because this molten solder while soldering one side of the PCB can damage components on the other side. After this, the PCB is moved for the final inspection.
Step 6: Final Inspection and Functional Test
Now the PCB is prepared for testing and inspection. This can be the functionality test, where electrical signals and power supply are given to the PCB at the desired pins, and output is checked at the desired test points or output connectors. This test requires common lab instruments like oscilloscope, DMM, and function generator This test is to test the functionality and electrical characteristics of PCB and to verify current, voltage, analog, and digital signals as described within the requirements of PCB AND circuit design If any of the parameters of the PCB shows unacceptable results, then the PCB is discarded or scrapped as per the corporate standard procedures. The testing phase is extremely important because it determines the success or failure of the complete process of PCBA.
Step 7: Final Cleaning, Finishing and Shipment
Now that the PCB is tested and declared OK from all aspects, it’s time now to wash the unwanted residual flux, finger dirt, and oil stains. A stainless-steel-based high washing tool using deionized water is sufficient to scrub all sorts of dirt. The deionized water won’t damage the PCB circuit. After washing the PCB is dried with compressed gas. Now the ultimate PCB is prepared for finish off and shipment. After all, products are produced, they’re packaged and shipped in step with customer needs. PCBA electronic product processing may be a relatively complicated process. Within the process of production, each employee must work together and strictly follow the assembly process to manage the standard, meet the customer’s quality requirements, and deliver the right product.
After The PCB Assembly Process
Suffice it to mention, that the PCB assembly process is a grimy one. Soldering paste leaves behind some amount of flux, while human handling can transfer oils and dirt from fingers and clothing to the PCB surface. Once all is finished, the results can look a bit dingy, which is both an aesthetic and a practical issue. After months of staying on a printed circuit board, flux deposition starts to smell and feel damp. It also becomes somewhat acidic, which might damage solder joints over time. Additionally, customer satisfaction tends to suffer when shipments of recent PCBs are covered in residue and fingerprints. For these reasons, washing the merchandise after finishing all the soldering steps is vital.
A stainless-steel, high-pressure washing apparatus using deionized water is that the best tool for removing residue from PCBs. Washing printed circuit boards in deionized water pose no hazard to the machine. This can be because it is the ions in regular water that do damage to a circuit, not the water itself. Deionized water, therefore, is innocuous to the printed circuit boards as they experience wash cycle. After washing, a fast-drying cycle with compressed gas leaves the finished PCBs ready for packaging and shipment.