Neurochrome delivers high-performance, quality products which are designed and manufactured to last. Quality in audio circuits manufacturing impacts both the performance of the product and its reliability. At Neurochrome, I have selected North American manufacturers and suppliers who share my values of respect for human working conditions and the environment.

PCB assembly examples

The image above shows three examples of printed circuit board assembly. The first two examples show some of the common issues with low-cost overseas assembly including solder splatter, flux residue, and haphazardly installed components. The third example shows a typical Neurochrome board manufactured and assembled in Canada. The difference in quality is obvious even to the naked eye.

Neurochrome’s circuit modules are made in Canada by manufacturers who specialize in small and medium sized, high-quality production runs. My printed circuit board (PCB) blanks are manufactured in Toronto, Canada. The boards undergo a complete electrical test before they ship. I source the electronic parts either directly from the manufacturers or from authorized distributors in the US and Canada and hand-deliver them to my assembly manufacturer in Calgary, Canada. This ensures that Neurochrome products contain only genuine parts.

The PCB assembly process, i.e. the placing and soldering of the parts onto the blank circuit board, has great impact on the performance of the final product. For good audio performance it is essential that the assembly is free of contaminants like flux and solder residue. Such contaminants will cause leakage currents on the surface of the PCB which drastically increase DC offset and often increase distortion as well. Many of these contaminants are hydrophilic and will absorb moisture from the surrounding air. The resulting corrosion will degrade the reliability of the assembly. Furthermore, the contaminants can cause electrochemical migration, i.e. the formation of new connections due to dendritic growth of tin whiskers. The importance of a clean workflow in the assembly process cannot be understated.

 Another important factor for audio performance is the quality of the solder joints connecting the parts to the conductive traces on the PCB. When a solder joint is made, the solder forms a metallurgical bond with the conductive trace and the component terminal. A solid solder joint should use just enough solder to form a strong metallurgical bond and ensure a reliable electrical connection.

It is especially in the area of PCB assembly that the domestic manufacturers excel. Seven steps are involved in the assembly process used by my Canadian assembly manufacturer:

  1. The moisture levels of the electronic parts and materials are monitored during the assembly process, which prevents micro-cracking of parts and components.
  2. All contaminants are removed from the circuit board.
  3. Solder paste is deposited and inspected by a 2.5D automated optical inspection (AOI) system. Lead-free solder is used to ensure that the PCB assemblies are RoHS compliant.
  4. The surface mounted parts are placed automatically and correct part placement and polarity is verified by 2D AOI.
  5. The PCB is heated following a prescribed temperature profile to reflow the solder. Following the correct temperature profile is crucial for an IPC-A-610 Class 3 level assembly.
  6. The PCB assembly is cleaned to remove flux residue (see Water-Soluble Flux below).
  7. The assembly is then inspected using 3D AOI which verifies correct part placement and orientation on the final PCB assembly. The 3D AOI also quantifies the quality of each solder joint. Solder joints that are hidden from view, such as connections to thermal pads on the bottom of ICs, may be inspected by X-ray.

Each of these steps is critical for a quality end product. You will be hard pressed to find an overseas manufacturer that can offer comparable quality at this price point.

The IPC-A-610 Standard for PCB Assembly

Circuit board assembly is governed by the IPC-A-610 standard (Institute of Printed Circuits – www.ipc.org). This standard contains three assembly classes as shown below.

Class 1 Class 2 Class 3
Electronic Product Category General Dedicated service High-performance / Harsh environment
Main Focus Cost Minimum service disruption No service disruption
Product Life Cycle Short Long Very long, mission-critical
Examples Toys, LED lighting, low-end audio electronics Computer servers, laptops, high-end audio electronics Automotive, aerospace, military, medical

Neurochrome’s Canadian assembly manufacturer employs advanced-class equipment and finely controlled processes. They guarantee the final assembly will meet IPC-A-610 Class 2. However, in a recent analysis of one of my builds, they found that more than 99.9% of all solder joints met the IPC-A-610 Class 3 standard. This far surpasses the standard of most consumer electronics which are commonly produced to IPC-A-610 Class 1.

Water-Soluble Flux

Cleanliness in the PCB assembly process is crucial to ensure high-end performance and long service life of the assembled circuit. I chose an assembly manufacturer who uses an optimized aqueous workflow, which includes the use of water-soluble flux. This ensures that all contaminants are easily cleaned off the circuit board after assembly. The manufacturer takes the cleanliness a step further by using Zestron Hydron, an environmentally friendly cleaning agent.

Custom Solder Paste Stencil Design

Solder is used to form a strong metallurgical bond between the circuit board trace and the end cap of the electronic part. For a strong and lasting bond, the solder must properly wet the conductive parts and an inter-metallic compound layer must form before the solder is allowed to cool. The finished joint should be a smooth, concave fillet of solder which meets the conductive surfaces at an acute angle. A smaller contact angle will result in lower stress within solder joint and make the joint more resistant to failure (Lee, 2001).

Precise control of the amount of solder used in electronics assembly is key; both for the circuit performance, its longevity, and for the environment. Neurochrome’s assembly manufacturer optimizes the amount of solder used with a custom designed solder paste stencil. The stencils used in the assembly are designed specifically for the Neurochrome boards and are optimized to match the circuit boards and the electronic parts. They are critical to the performance of the final product.

References

Lee, N.-C. (2001). Reflow Soldering Processes. Elsevier.