PCB Manufacturing Process
The PCB (Printed Circuit Board) manufacturing process is intricate, involving numerous sequential steps. Different types of PCBs—such as single-sided, double-sided, and multilayer—require distinct manufacturing procedures. Here, we will focus on the PCB manufacturing process for a typical multilayer PCB, which consists of multiple conductive layers stacked together with dielectric layers in between.
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What is the PCB Manufacturing Process?
The PCB manufacturing process encompasses several key stages: designing the circuit layout, transferring the design onto a copper-clad substrate, etching to create circuit patterns, drilling for component placement, electroplating to establish connections, applying solder-proof film, printing screen labels, and conducting electrical tests and inspections. Understanding the PCB manufacturing process is crucial due to its widespread application in various industries and everyday life.
How is the PCB Manufacturing Process Carried Out?
Pre-production Engineering (DFM)
Before manufacturing begins, front-end engineers review the customer’s electronic data, including fabrication drawings and specifications. They work on converting this design data into manufacturing data according to industry standards. Any design-related queries are resolved with the customer before finalizing manufacturing instructions, which guide the entire PCB production flow.
Substrate Cutting
In the PCB manufacturing process, the raw material is cut to the size of the production panel. For multilayer PCBs, this raw material is a thin copper-clad laminate, also known as the core.
Inner Layer Preparation
The core material is cleaned to remove contaminants. A photoresist film is applied to the copper-clad laminate and exposed to UV light in a yellow room. The exposed areas of the photoresist film harden, while unexposed areas remain soft. After exposure, the panel is developed using a chemical that removes the unhardened photoresist, leaving behind a hardened circuit pattern that protects the copper during etching.
Inner Layer Etching
During etching, the unprotected copper areas are removed, leaving the circuit pattern intact. The inner layers are then inspected using Automated Optical Inspection (AOI) to detect shorts and defects. The treated inner layers undergo brown oxide treatment, which cleans the panel and enhances adhesion before moving to the lamination stage.
Lamination
The lamination process involves assembling copper foil, inner layer cores, and prepreg to form the panel. Accurate alignment is achieved using punched targets and tooling. High heat and pressure in a lamination machine bond the layers permanently. After lamination, excess prepreg is milled to shape the panel.
Drilling
Following lamination, the panel, now resembling a double-layer PCB, is drilled using a machine. This machine pins the panel and drills tooling holes for alignment. Panels are drilled simultaneously based on the manufacturer’s capability. Small vias may require laser drilling due to the high breakage rate of mechanical drilling.
De-Burring
High-speed CNC machines can create burrs around drilled holes, which must be removed before electroplating. A deburring machine cleans the panel using high-pressure water to eliminate dust and burrs.
Electroless Copper Plating
Panels are then placed on racks and passed through chemical baths to apply a thin layer of electroless copper in the holes. This initial copper layer provides a base for further plating.
Pattern Imaging
The panels are cleaned and laminated with a dry film that is sensitive to light. The dry film is exposed to UV light in a clean, dust-free room, and advanced manufacturers use Laser Direct Imaging Systems (LDI) for precise patterning. The film is developed, and the panel is inspected for defects.
Copper Pattern Plating
In this step, the panels are plated with copper by passing them through chemical baths. The plating thickness is typically 0.0012” on the surface and in the holes. The panel is then electrodeposited with tin to protect the copper during the etching process.
Strip Etch Strip
Panels undergo a resist stripping process where the dry film is removed, and the remaining copper is etched away. Etching is carefully controlled to avoid over- or under-etching. A microscope is used to ensure trace widths are correct. The tin resist is then stripped from the panel.
Automatic Optical Inspection (AOI)
The final inspection is performed by AOI machines, which visually scan the etched panel to detect any deviations from the original design. The AOI system ensures that no shorts or defects are present.
Solder Mask
A solder mask, or solder resist, is applied to the panel’s surface. This non-conductive coating is imaged and developed to create openings for soldering. The panel is then cured in an oven at high temperatures.
Silkscreen
Silkscreen, or legend, is printed on the panel using thermal ink, commonly in white. Modern PCB production often uses digital printing machines instead of traditional screen printing for added precision.
By understanding and optimizing each stage of the PCB manufacturing process, you can ensure high-quality and reliable PCBs suited for various applications.
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