How to Transform Raw Materials into a PCB: A Step-by-Step Guide

PCB circuit boards are integral to virtually all electronic products, from large-scale items like airplanes and rockets to smaller gadgets like headphones and watches. Hardware engineers deal with PCBs and PCB design daily. But what exactly is the process for a PCB to transform from raw materials into the design outlined in our files? Let’s explore this process step by step through a series of animations today!

01 Gerber File Import

To produce a qualified PCB, the first step involves input, typically referred to as a Gerber file. Upon receiving a client’s Gerber file, a factory doesn’t just proceed with manufacturing outright due to the significant risks involved. Instead, the factory utilizes DFM (Design For Manufacturability) software and, based on its manufacturing capabilities, makes certain optimizations. Of course, these optimization parameters must be communicated with the client to ensure they meet the design requirements.

02 Panelization

Often, hardware engineers will panelize boards themselves before sending them off for fabrication. This approach assumes a comprehensive understanding of the manufacturing process. Panelization isn’t merely for aesthetics or to simply enhance assembly efficiency; it’s also about meeting production needs. Some PCBs are too small to meet the requirements for fixtures, necessitating their combination for production. Panelization typically includes the addition of process edges, and experienced factory engineers may also optimize material utilization, especially for boards of unusual shapes. For example, at quick-turn factories like JLCPCB, the primary goal of panelization is to maximize material utilization to reduce costs.

03 Material Cutting

The standard material used is a 2089*1246 double-sided copper-clad laminate, with various models of copper foil thickness available. Typically, the copper foil thickness is 0.035mm. The core material sandwiched between the copper layers is usually composed of epoxy resin and glass fiber cloth, commonly referred to as FR4. Besides FR4, substrate materials can also include paper-based and aluminum-based materials, among others. These materials are cut to the required sizes using a machine known as a cutting machine, followed by a series of edge-finishing processes.

04 Positioning Holes

Before proceeding with subsequent processes, positioning holes are drilled at both ends of the substrate. The purpose of these holes is to fix and identify the relative position of the substrate during the later stages of manufacturing.

05 Drilling

Three types of holes are drilled into the substrate for different purposes:

1. Holes for screws, used for mounting.

2. Reserved holes as per customer requirements.

3. Vias for electrical connectivity between circuit layers.

An automatic drilling machine selects and changes drill bits of various sizes according to the specifications, with the smallest drill bit size reaching down to 0.2mm.

06 Board Scrubbing

The primary purpose of board scrubbing is to address surface cleanliness and roughness issues. This process involves removing oxidation and increasing the roughness of the copper surface to enhance the adhesion of the photoresist to the copper.

07 Copper Plating (PTH)

The copper plating process line is typically quite extensive, with reports of JLCPCB’s line reaching 190 meters in length. The principle behind the copper plating process is straightforward. After drilling, the boards are immersed in a special solution to activate the material of the hole walls, similar to how solder paste facilitates the adhesion of solder to various materials. This activation process makes the hole walls more receptive to copper ions. The boards are then soaked in a chemical solution containing copper ions, allowing these ions to deposit on the surface of the hole walls and form a conductive layer, thereby achieving conductivity between the copper layers above and below.

08 Lamination + Exposure + Development

Lamination: The treated substrate is covered with dry or wet film through thermal pressing or coating, preparing it for subsequent exposure.

Exposure: The substrate with the applied film is aligned with a negative, and under an exposure unit, ultraviolet light is used to transfer the negative pattern onto the photosensitive film.

Development: Using a developing solution (sodium carbonate), the unexposed film is dissolved and washed away, while the exposed parts are retained.

09 Electroplating + Etching

Why is electroplating necessary? After the processes mentioned above, the copper foil that needs to be retained on the copper-clad board is fully exposed. The electroplating process involves coating these exposed copper foils with a layer of tin to protect them from being accidentally removed during the subsequent etching process. After electroplating, the boards go through a film removal machine to clean off the previous coating, and the unwanted copper foil is etched away, leaving behind the copper foils that were coated with tin. Finally, a tin stripping machine removes the tin, leaving behind the desired copper foil.

10 Automatic Optical Inspection (AOI) + Impedance Testing

AOI equipment is used for optical scanning of the manufactured PCBs, comparing the scan results with the customer’s original design to ensure the PCB fully meets the client’s specifications.

Impedance testing is conducted to ensure the continuity of each circuit, further assuring the quality of the PCB.

11 Solder Mask + Silkscreen

The solder mask, often referred to in casual conversation, is applied after the processes outlined above. To transform the PCB into the various colored boards we commonly use, a layer of solder mask ink is applied. While green is the most common color, there are many options available, including yellow, white, purple, and black. After applying the solder mask, silkscreening is done on the board to add customer-required markings, typically including component locations and version numbers.

12 Board Separation + Flying Probe Testing + Cleaning + Packaging

At this point, the PCB is essentially complete. It undergoes flying probe testing to check for continuity and any potential shorts. Then, the boards are either separated or subjected to V-CUT, followed by another round of cleaning. Finally, the PCBs are packaged and shipped to the customer.

Conclusion

The various processes outlined cover most of the manufacturing steps from substrate to finished PCB, though some steps, like drying after each cleaning and exposing copper after applying the solder mask, are briefly mentioned. While manufacturing processes may vary slightly from one factory to another, this article aims to provide readers with a clear understanding of the journey a PCB takes from conception to completion.

FAQ

  1. What is the purpose of panelization in PCB manufacturing?

Panelization in PCB manufacturing serves multiple purposes beyond mere aesthetics or improving assembly efficiency. It is primarily done to meet production needs, especially for small PCBs that do not meet fixture requirements and thus need to be combined for production. Panelization also includes the addition of process edges and, in the case of experienced manufacturers, may optimize material utilization, particularly for boards with unusual shapes. The overarching goal is to maximize material use, thereby reducing costs, a practice notably employed by quick-turn factories like JLCPCB.

  1. Why is electroplating important in the PCB manufacturing process?

Electroplating is a critical step in PCB manufacturing because, after certain processes like drilling and copper plating, the copper traces that need to be preserved are fully exposed. The electroplating process involves coating these exposed copper traces with a layer of tin to protect them from being inadvertently etched away in the subsequent etching process. This step ensures that the necessary copper traces are preserved while the unwanted copper is removed, ultimately leaving behind the desired circuit patterns on the PCB.

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