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What Makes a PCB Assembly Complex and How to Solve

complex PCB assembly
pcbonline PCBONLINE Team Mon, Apr 24, 2023

As electronics technology improves, complex printed circuit board (PCB) assembly services for electronics manufacturing get more efficient and affordable. In this blog, we'll teach knowledge about complex PCB assembly. Let's jump into it!

What Makes a PCB Assembly Complex?

complex PCB assembly

Regarding complex PCB assembly, the first thing to know is what makes a PCB assembly process complex.

You should know that the PCB assembly process for all rigid PCBs is the same, no matter how many layers they have or what components to be mounted. The surface-mount (SMT) and through-hole (THT) assembly for all rigid PCBs follow the same procedures.

However, a PCB assembly can be complex due to the mounting of BGA and QFN. And PCB assembly for Bluetooth, WiFi, and communication modules is complex.


We'll analyze them individually and show you how we solve them!

Complex PCB Assembly for BGA and QFN

BGA is a ball grid array, and QFN is a quad-flat no-lead. They are all integrated circuits (ICs) that are difficult to mount on PCBs. BGAs have a grid array of solder balls at the bottom, and QFNs have right-angle pads all around them. During PCB assembly, we can't see the BGA and QFN soldering effect through the naked eye.

Moreover, for BGA and QFN PCB assembly, it is easy to cause soldering defects, such as solder bubbles, cold solder, non-wetting, and de-wetting.

How do we ensure the success of BGA and QFN PCB assembly? The advanced PCB assembly supplier PCBONLINE makes some efforts to PCB stencil design.

For BGA PCBs, it is suggested to design the BGA openings on the stencil to be square and a little bit larger than the PCB pads instead of matching them.

    BGA PCB stencil

Only an X-ray machine can inspect the BGAs. The X-ray hits the BGA bottom, showing the solder balls so that we can compare them with the reference to make sure they are qualified for reflow soldering.

Besides, during PCB assembly, we have an X-ray inspection before reflow soldering to ensure the solder balls of BGA PCBs are adequate for soldering.

Complex PCB Assembly for Bluetooth, WiFi, and Communication Modules

Bluetooth, WiFi, and communication modules are commonly used modules in electronics. But the PCB assembly for them can be tricky. The reason lies in the half-holes on the edges of the boards.

Because of the half holes all around the Bluetooth, WiFi, and communication modules, it is uneasy for solder paste to wet the PCB pads, which can cause cold solder.

half hole PCBA

For PCBA modules with half holes, it is suggested to design a step-up or Nano stencil for PCB assembly. By using such a special SMT stencil, more solder can wet the half-hole pads. In this way, we can make successful PCB assembly for the Bluetooth, WiFi, and communication modules.

If the modular PCBA has no BGA, we do not have an X-ray inspection, and the SMT assembly process is the same as the assembly for other rigid PCBs.

Complex PCB assembly process

For all rigid PCBs, including FR4 PCBs, MCPCBs, ceramic PCBs, and PTFE high-frequency PCBs, the PCB assembly process is the same. The SMT steps include solder paste printing > solder paste inspection > placing SMDs on PCB > (X-ray inspection for BGA >) reflow soldering > automatic optical inspection. The THT steps are inserting THT component pins through PCB holes > wave soldering > trimming component pins.

You can check the PCB assembly process in the below video.

For complex PCB assembly, the only difference between FR4 PCBs and aluminum PCBs is the reflow soldering temperatures.

For example, aluminum PCBs typically can withstand reflow temperatures between 200°C and 260°C. By contrast, for ceramic PCBs, typically made of ceramic materials such as alumina or aluminum nitride, the reflow temperature is generally between 160°C and 250°C.

For flexible PCBs and rigid-flex PCBs, their PCB assembly requires a jig or fixture to fix them during the whole PCB assembly process.

Features of Complex PCB Assembly

Complex PCBs can be multilayer FR4 PCBs, copper base PCBs, ceramic PCBs, etc. Compared with easy FR4 printed circuit board assembly, complex PCB assembly can feature fine pitch, smaller or larger components, BGA/DFN, and half holes.

For PCB assembly for high-end applications, such as automotive, aerospace, defense, and medical electronics, the PCB assembly level has to be IPC-A-610 Class 3. And the complex PCB assembly may need a conformal coating to lengthen the lifespan of the PCBA.

Complex PCB Assembly from A to Z

PCBONILNE is a one-stop PCB assembly manufacturer for middle and high-end applications. Founded in 1999, it has two advanced PCB manufacturing bases and one PCB assembly factory. It offers complex PCB fabrication and assembly from prototypes to massive production.

By working with PCBONLINE for complex PCB assembly, you can enjoy many benefits:

  • One-stop complex PCB assembly including PCB fabrication, PCB assembly, and post-assembly testing and services.
  • Free one-on-one engineering support, Gerber and BOM check, and PCBA design for assembly (DFA).
  • BOM component sourcing from original factories and direct suppliers that have been audited.
  • Most affordable complex PCB assembly from source factory manufacturer.
  • Comprehensive PCBA testing and value-added services such as functional testing, IC programming, conformal coating, thermal aging, box build assembly, and application simulation testing.

PCBONLINE has rich complex PCB assembly experience for industrial, automotive, aerospace, defense, computing, communication, medical, agricultural, and consumer electronics. If you have any complex PCB assembly needs, send your Gerber and BOM to info@pcbonline.com to get a quote.


If your PCBA has BGA or QFN, or if it is a Bluetooth, WiFi, or communication module with half holes at the edges, it is a complex PCB assembly. If your PCB is flexible or ceramic-substrate, the PCB assembly can also be called complex PCB assembly. The A-Z PCB assembler PCBONLINE can design the SMT stencil and reflow profile adequate for complex PCB assembly. If you need complex PCB assembly, this source factory manufacturer won't let you down.

© This article is an original work of the PCBONLINE team. Please indicate the author PCBONLINE if you reprint. If the article is reproduced without permission or indicating the author's source, PCBONLINE reserves the right to investigate the infringement.


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