Optimizing Complex PCB Assembly for Superior Quality​

Relying on the industry’s most professional team to complete high-quality PCB assembly, our products cover aerospace, medical and other high-end equipment.

Welcome to LST, your premier destination for high-end complex PCB assembly, PCB box build assembly services, and through hole PCB assembly solutions. With over 18 years of industry expertise, we specialize in addressing your enterprise’s precision board, challenging board, and specialized circuit board manufacturing needs. Our commitment to excellence is reflected in our turnkey complex PCB assembly services, tailored to clients worldwide.

As an ISO9001 certified PCB assembly company, LST adheres to stringent operational standards, ensuring the delivery of top-quality services to our global clientele. Equipped with 8 SMT assembly lines capable of handling 0201 package parts, alongside 8 through-hole assembly lines and a team of over 300 skilled workers, we possess the capabilities to fulfill diverse customer requirements with precision and efficiency. Experience the difference with LST – where expertise meets excellence in complex PCB assembly, PCB box build assembly services, and through hole PCB assembly.

High Quality PCB Services

High-quality PCB Assembly
  1. Our high quality PCB assembly service is renowned for its excellence, especially in the fabrication of High-Density Interconnect (HDI) PCBs. These complex multi-layer boards demand precision and specialized equipment at every stage of manufacturing. We prioritize rapid prototyping and efficient delivery without compromising on quality. Rigorous Design for Manufacturability (DFM) testing is integral to our process, ensuring flawless production from inception to completion. Trust us for reliable and top-tier HDI PCB assembly solutions tailored to your project’s needs.

  2. Precision and efficiency define our approach to high-quality PCB assembly, particularly for intricate projects like High-Density Interconnect (HDI) PCB fabrication. Equipped with cutting-edge technology and expertise, we specialize in delivering top-tier results. Rapid prototyping and seamless delivery are our signatures, ensuring timely project completion while upholding the highest quality standards. Our comprehensive Design for Manufacturability (DFM) testing guarantees error-free production, providing you with dependable and superior HDI PCB assembly solutions for your projects.

High-quality PCB Assembly

At LST, we have over 10 years of experience in manufacturing and assembling high quality rigid-flex PCBs. No matter what type of PCB you need, you can rely on us. Our reputation for delivering high-quality rigid-flex PCBs is due to several factors. We offer multi-layer boards in a variety of materials to meet your custom needs.

For partial turnkey PCBA, we specialize in component sourcing and supply chain management, which is crucial for complex PCB assembly, ensuring top quality and timely delivery.

  1. Component Procurement and Supply Chain Management: Our team specializes in assisting clients in selecting the highest quality components, securing competitive pricing from trusted suppliers, and meticulously managing the supply chain to ensure timely delivery and quality control of required components. Moreover, we provide tailored procurement recommendations to meet specific project requirements. Particularly in cases involving complex PCB assembly, we pay close attention to the quality and compatibility of components to ensure smooth assembly processes.

  2. Quality Control and Testing: Throughout the PCBA process, we implement stringent quality control measures, encompassing visual inspection, functional testing, and more, to ensure that products meet clients’ specifications and quality standards. When dealing with complex PCB assembly, we intensify our focus on every detail and requirement to ensure the stability and reliability of the final product. Our quality control team boasts extensive experience and expertise, enabling timely detection and resolution of potential quality issues, thereby ensuring smooth project execution and high-quality delivery overall.

High-quality PCB Assembly

We offer flexible and customized turnkey PCBA services according to your project requirements: Full Turnkey PCBA: This involves all services in the PCB assembly process such as material and component sourcing, PCB manufacturing and assembly, quality control, shipping, and logistics. Partial Turnkey PCBA: This type of assembly allows the customer to handle part of the process.
Our excellent quality assurance processes and dedication to service make us the best choice for turnkey PCB assembly.

High-quality PCB Assembly

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Related Products

Our Abilities

Assembly TypesComponent TypesFiles Required for Quote and Production
SMT Assembly( with AOI inspection);BGA Assembly(with X-Ray inspection);Through-hole Assembly;SMT& Through-hole Mixed Assembly; Kit Assembly● Passives, smallest size 0201(inch)
● Fine-pitch chips to 0.38mm
● BGA (0.2mm pitch), FPGA, LGA, DFN, QFN with X-Ray testing
● Connectors and terminals
● Turnkey PCB Gerber RS-274X, 274D, or PCB Design file
● Turnkey PCB BOM (Bill of Materials, .xls, xlsx)
● Turnkey PCB Pick-N-Place file / XY file (for production only)
Quality InspectionComponents SourcingOrder Quantity
● AOI Inspection;
● X-Ray Inspection
● Voltage Test;
● Chip Programming;
● ICT Test; Functional Test
● Turnkey PCB Full turnkey (All components sourced by Yingstar);
● Turnkey PCB Partial turnkey;
● Turnkey PCB Kitted/Consigned
● Turnkey PCB 5pcs to 100,000pcs;
● Turnkey PCB From Prototypes to Mass Production
PCB TypesSolder TypesAssembly Lead Time
Rigid PCB
Metal core PCB;
Flex PCB;
Rigid-Flex PCB
Leaded; Lead-Free(Rohs);
Water soluble solder paste
From 8 hours to 72 hours when parts are ready

Steps required for complex PCB assembly


Step 1: Solder Paste Stenciling

The initial phase of the PCB assembly process involves the application of the solder paste stenciling technique. In this step, a PCB stencil is utilized to shield the circuit board, revealing only the sections designated for component mounting. This targeted approach facilitates the precise application of solder paste solely to the specific areas where components will be positioned.

To achieve this, a mechanical device securely holds the board and solder stencil in place. An applicator is then employed to deposit solder paste at predetermined locations, ensuring uniform coverage across all exposed areas. Upon completion of this step, the stencil is removed, leaving the solder paste accurately deposited in the intended locations.

Step 2: A Game of “Pick and Place”

Many medical electronic devices are either implanted in the human body or worn on sensitive organs. If these devices malfunction, such as by short-circuiting or burning out, they may cause secondary harm to the patient. Therefore, it is crucial to accurately place the components in the designated positions using precise equipment.

Implantable medical electronics, such as cochlear implants and artificial eyeballs, typically have many electronic components in their internal structure. However, smaller devices present challenges in the picking and placing process, making it more difficult to maintain precision. To achieve the high accuracy required for assembling PCB for medical cochlear implants, Robots are responsible for picking and mounting surface-mount components onto circuit boards, ensuring that the components are precisely placed on the solder paste with the mounting mechanism.

Step 3: Soldering Reflow

The reflow soldering process is tailored to enhance the connections between the circuit board and electrical components. In this method, a conveyor belt guides the circuit board through a sizable reflow oven. The solder paste undergoes melting as the PCB board is heated to approximately 2500 degrees Celsius during this process. Subsequent to the heating phase, the PCB passes through a sequence of coolers, aiding in the cooling and solidification of the solder paste. This results in robust connections between the electrical components and the board.

It’s crucial to emphasize that for double-layered PCBs, the stenciling and reflowing processes adhere to a specific sequence. The side of the board featuring fewer and more manageable electrical components is completed first in this meticulous order.

Step 4: PCB Assembly Test

We emphasize the importance of precision, reliability, and the critical nature of high-quality circuit boards. Therefore, identifying trustworthy manufacturers and top-notch PCBA facilities, coupled with the assurance of ISO 13485 certification, is crucial. Even if these standards are met, the PCB testing services must be scrutinized carefully.

In addition to the continuous manual inspection (including SPI and AOI) integrated into the production process, the final stage of medical PCB assembly also involves functional testing. This rigorous inspection ensures that the motherboard is functioning as expected and meets the strict standards set by the medical industry.

After testing, a comprehensive cleaning process is conducted to eliminate potential residue such as oil, flux, or other contaminants from the circuit board. Additionally, given the unique requirements of the product, customers may need to customize specialized PCB production processes for specific application types, such as sterile processing.

Common Problems in Complex PCB Assembly and Solutions

Defective PCB Packaging As we mentioned, it is crucial to verify the Bill of Materials (BOM) to ensure the correct packaging is linked to the parts. However, the examination of the PCB packaging must go beyond the BOM itself. It is important to verify that the packaging is correctly constructed according to the manufacturer’s datasheets and industry standards.

The packaging pads should also be checked to ensure that the components can be properly mounted and soldered onto the PCB board.

Insufficient Personnel Access If rework technicians do not have enough workspace, it becomes challenging to replace parts, fix any assembly defects, or test the circuit boards. The limitation of space leads to longer PCB assembly times and higher costs because technicians need to navigate around obstacles and may damage other components. Furthermore, if such connectors and other forms of human-machine interfaces are not conveniently accessible, connecting the board to its system may pose challenges.

Poor Soldering Besides leaving adequate space for pick-and-place machines, components must also be precisely positioned to prevent soldering errors. For wave soldering, it is necessary to rotate the workpiece to enter the wave crest perpendicular to it.

Additionally, avoid placing taller components in front of shorter ones in the wave crest, as this can cause a shadow effect, weakening the solder joints on those pins. Before putting smaller 2-pin items into the reflow oven, ensure both pins are thermally balanced. By doing so, you can prevent the tombstoning phenomenon, where a component is pulled up onto one pin because one side heats up faster than the other.

Bill of Materials Issues Inaccuracies in the Bill of Materials can lead to the ordering and installation of incorrect parts on the circuit board. The BOM may also contain outdated information and list parts that are no longer producible.

Before sending the circuit board for manufacturing, please check the BOM of the circuit board for:

  • Parts with matching part numbers and descriptions
  • A PCB layout that precisely matches its components
  • Parts that may be difficult to obtain due to end-of-life, obsolescence (OBS), and parts recommended for new designs DFM Errors An important aspect of designing circuit boards is Design for Manufacturability (DFM). Ensure components maintain proper positioning, and there is adequate spacing between them, the edges of the circuit board, and any other mechanical objects on the circuit board.

Without this spacing, it may not be possible to use automated machinery to assemble components, which would significantly increase the manufacturing cost and time of the circuit board.

Defective PCB Packaging As we mentioned, verifying the BOM is crucial to ensure the correct packaging is linked to the parts. However, the examination of the PCB packaging should not be limited to the BOM alone. Verify that the packaging has been correctly constructed according to the manufacturer’s datasheets and industry requirements. The packaging pads should also be checked to ensure that components can be properly mounted and soldered onto the PCB board. Based on this, modifications should be made for a more professional response to the “Problems Encountered in Complex PCB Assembly and Rejection Methods.”

How to choose a high quality PCB assembly manufacturer

First, the qualification certification of the manufacturer

Choosing a high-quality PCB manufacturer should first focus on its qualification and certification. Qualified PCB manufacturers usually have ISO9001 quality management system certification, ISO14001 environmental management system certification and UL certification. These certificates prove that the manufacturer in the quality management, environmental protection and product safety has a certain ability and experience, is an important reference index for selection.

Secondly, you can also pay attention to whether the manufacturer has obtained some industry associations and honors, such as IPC certification, electronics association members. These certifications and honors are also an important basis for assessing the strength and reputation of manufacturers.

Second, production equipment and processes

High-quality PCB manufacturers usually invest a lot of money to buy advanced production equipment and advanced labor. Advanced equipment and processes can improve production efficiency and product quality, to ensure the accuracy and stability of the circuit board.
You can focus on whether the manufacturer has automated production lines, high-precision cutting machines, gold-plating equipment advanced equipment, and to understand its production process is in line with international standards. In addition, you can also find out whether the manufacturer has an independent R & D team, able to customize the design and production according to customer needs.

Third, the quality control system

Select high-quality PCB manufacturers also need to pay attention to its quality control system. A perfect quality control system can be the stability and reliability.
You can learn whether the manufacturer has a strict quality control process and standards, whether there is a specialized quality control team to supervise and inspect. In addition, you can also find out whether the manufacturer has carried out comprehensive quality management training to improve the quality awareness and technical level of employees.

Fourth, customer reviews and word of mouth

The quality and service of PCB manufacturers can be assessed through customer reviews and word-of-mouth. You can check the manufacturer’s official website, social media, and industry forums to learn more about other customers’ reviews and feedback about the manufacturer.
You can pay attention to the customer’s evaluation of the manufacturer’s product quality, delivery time, after-sales service and other aspects, as well as whether there are quality problems and disputes. In addition, you can also find out whether the manufacturer has long-term cooperation with large customers, which is also an important reference for evaluating the strength and credibility of the manufacturer.

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