Step-by-Step Guide to PCB Assembly Process
PCB Assembly, or PCBA, is the intricate process of assembling and soldering all components and connectors onto a circuit board. As component sizes shrink, pin density increases, and product iterations accelerate, conventional manual techniques struggle to meet the demands of this evolving landscape. In the business arena, vertically integrated electronic manufacturing enterprises find it challenging to keep pace with the swiftly changing times. This is where companies like FS Technology, specializing in PCB assembly services, become indispensable. In this article, FS Technology will illustrate how our digitized smart factory streamlines the PCB assembly process.
PCB Assembly Process Tutorial
The flowchart depicted above illustrates the intricate PCBA manufacturing process in its entirety, encompassing a range of tests and rework procedures. The objective of this article is to assist readers in gaining a clearer understanding of the PCB assembly process. To facilitate this, the explanation is organized into four main phases and several sub-stages, presented in a sequential order for enhanced comprehension.
Stage 1: Design and Manufacturing
The design phase is a key step where designers translate concepts into reality. This process involves using design software such as Altium, Protel, Orcad, KiCad, to create circuit patterns and generate manufacturing and assembly files. Although this stage doesn’t directly involve assembly, it is closely intertwined with it, defining how assembly should be carried out, which components are to be assembled, and their specific locations.
Manufacturing entails producing bare boards, transferring circuit patterns onto physical boards through PCB manufacturing processes, ultimately incorporating the required paths and drill holes. The PCB bare board serves as the essential platform for assembling components, constituting the main body of the PCBA board.
Stage 2: Material Preparation
In this phase, it is vital to have all the required materials for assembly, encompassing, but not limited to:
- Components: The essential elements that bring functionality to the PCBA board, procured in accordance with the BoM file.
- Solder Paste: Employed for soldering components, forming robust solder joints.
- Solder Alloys: Some designs may necessitate solder alloys in addition to solder paste.
- Flux: Utilized to enhance assembly quality, it can deoxidize, clean, improve wetting, and promote adhesion.
- Stencil: Integral in SMT processes for solder paste application, manufactured based on design files.
- Equipment: Encompassing machines for surface mounting, soldering, testing, and desoldering.
Stage 3: SMT Process
SMT currently holds the position as the primary assembly technique. In line with the trend towards miniaturization, more components are increasingly adopting surface mount devices. This approach allows for denser layouts and assembly. The SMT assembly process is outlined as follows:
Step 1: Solder Paste Printing
Solder paste is evenly applied to a pre-fabricated stencil. Subsequently, a blade sweeps across the stencil, causing the solder paste to drop onto the designated positions on the PCB.
Step 2: SMD Patch
A pick-and-place robot is loaded with the component file to mark the positions of the components. Subsequently, it selects the corresponding components based on the file instructions and installs them into the specified locations.
Step 3: Reflow Soldering
After surface mounting, the PCBA enters a high-temperature reflow oven, employing the reflow soldering method due to the SMT process. The entire process goes through stages of preheating, temperature ramp-up, soldering, and cooling. Ultimately, the components are securely fixed onto the board.
Stage 4: THT Process
For through-hole components, FS Tech typically employs a plug-in machine. If the component size is too large or for expediting prototype manufacturing, manual assembly and soldering may be utilized.
Step 1: Plug-in Machine
The equipment used for automated plug-in closely resembles the pick-and-place machines in the SMT process. It involves inserting the component pins into through-holes and applying solder.
Step 2: Wave Soldering
Due to through-hole assembly involving large components and connectors that require stronger mechanical connections, wave soldering is used, which results in a larger solder joint after soldering.
Step 3: Manual Soldering
Although FS Tech’s assembly facilities are equipped with a substantial amount of automated machinery, manual soldering can expedite production speed for small batches or prototype projects.
After PCBA Manufacturing Process
After the completion of the PCB assembly process, a flawless PCBA board is born. For some DIY enthusiasts, this marks the end of all procedures. However, for manufacturers, additional efforts are required post-assembly to ensure both quality and aesthetics.
Firstly, manual inspection is crucial, emphasizing more on it after the manufacturing of PCBA. During the initial stages of the PCBA project, both parties involved in the collaboration negotiate the contract terms to ensure the smooth progress of the project. One crucial aspect is determining the applicable standards. The collaboration partners clearly define which official standard the project adheres to, serving as the ultimate acceptance criteria that delineates what issues are tolerable and what is deemed a defect. As an example, FS Tech typically adheres to IPC-610-A-G in the absence of specific requirements. This implies that most defects are not permissible, with only those affecting aesthetics and not performance being tolerated. Given that high-temperature processes and machine automation in assembly may lead to common PCB problems such as solder bridging and cold solder, engineers perform post-assembly sampling inspections to identify and assess issues against the final acceptance criteria.
After confirming the assembly quality, these PCBA boards undergo cleaning. This process aims to enhance aesthetics and, more importantly, eliminate surface residues. Chemical agents like flux and solder paste are used in the PCB assembly process. While these residues pose no immediate threat to the board, prolonged storage in a humid environment can lead to the combination of ionic contaminants and organic residues with water molecules, resulting in corrosion. When these problematic boards are eventually put into use, the consequences may include circuit leakage or extensive damage.
Finally, PCB testing services are customized based on customer requirements. In addition to routine functional tests, we offer various options such as drop tests and aging tests. Some tests are complimentary, while others may incur additional charges based on customer preferences.
Considerations in the PCB Assembly Process
In the realm of business activities, the entire assembly process is intricate and tedious. Any error in this process can result in efforts going to waste. To address this, FS Tech offers key considerations for PCB assembly. On one hand, this aims to assist you in enhancing the efficiency of your projects, and on the other hand, it showcases FS Tech’s professionalism in PCBA projects.
DFM/DFA
This presents two design approaches, where DFM aims to ensure that the design considers feasibility, cost-effectiveness, and efficiency in its PCB manufacturing process. On the other hand, DFA focuses on optimizing the PCB assembly process. No one wishes to assemble a batch of unsuitable or defective PCBA boards, and certainly, no one wants assembly to be affected by issues from the design stage. FS Tech utilizes DFM and DFA for device analysis, pin analysis, pad analysis, and other measures to optimize assembly steps, reduce components, and enhance the probability of successful assembly.
Material Inspection
At the heart of PCB assembly lies the core process of installing electronic components onto the board. For this, there are three main material components: the PCB, components, and assembly materials.
Concerning the PCB, if you opt for FS Tech’s turnkey service, all issues from PCB manufacturing to assembly will be handled by us. However, for assembly projects, we need to inspect your PCB board to ensure their qualification, and responsibilities will be allocated accordingly.
Regarding components, you can either procure them independently or entrust FS Tech. For components procured independently, we take certain measures. We recommend utilizing FS Tech’s component procurement service, where we source from reliable, long-term partners. This not only saves your time but also capitalizes on economies of scale to reduce costs.
As for assembly materials, they are stored in FS Tech’s assembly facility, awaiting your orders. As a socially responsible PCBA company, we ensure that the materials used comply with RoHS directives.
To set FS Tech apart from other assembly companies, we have established a dedicated quality inspection department responsible for incoming material assessment for the PCB assembly process. The engineers in this department are responsible for the following:
- Verifying the quantity and model of the BOM list
- Conducting sample tests using multimeters and test benches
- Checking for deformities, oxidation, or damage in complex components
Consolidated
Unified Code: To avoid misplacement and facilitate management, a unique identifier is assigned to the front of the PCB before assembly.
Handle with Care: When transporting the assembled PCBA, exercise caution and use protective measures such as antistatic bags. When placing them, isolate or position two PCB boards back-to-back.
Wear Gloves: On one hand, human static electricity poses a threat to components, and on the other hand, the oils from fingerprints may lead to corrosion.
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