How Inner Layer Residual Copper Rate Affects PCB Thickness and Quality
4 min
- How Inner Layer Copper Affects Board Thickness
- Importance of Residual Copper Rate
- The Role of PP Sheets in Multilayer Lamination
- Consequences of Low Residual Copper Rate
- JLCPCB Recommendations
- Common Issues in Gold Finger Design
- Common Issues in PCB Gold Finger Design
In printed circuit board (PCB) manufacturing, precision is crucial for maintaining quality and performance. One key factor that significantly influences PCB quality is the residual copper rate in the inner layers. This concept becomes particularly critical in multilayer PCBs, where the balance of copper distribution impacts the final board thickness. This article explores how the inner layer residual copper rate affects board thickness and the importance of optimizing this rate to ensure robust and reliable PCBs.
How Inner Layer Copper Affects Board Thickness
As shown in the diagram, when the copper coverage in the inner layer is minimal, the (PP prepreg) sheets, regardless of their thickness, must spread evenly to fill the gaps between layers. Once the PP sheets cool and solidify, the reduced resin volume leads to a thinner overall board thickness.
Importance of Residual Copper Rate
So, how much copper should be laid in the inner layer to ensure that the board thickness doesn’t fall below tolerance limits? This is where the "residual copper rate" comes in. The residual copper rate refers to the percentage of the inner layer's copper circuit patterns relative to the entire surface area of the board.
Residual copper rate = the area of copper in the current layer / total area of the board.
The Role of PP Sheets in Multilayer Lamination
In multilayer board lamination, PP sheets are cut into pieces and placed between the inner core board and another core board, or between the core board and copper foil. The resin on the PP melts under high temperature and pressure, filling the copper-free areas on the core board. After cooling, the resin solidifies, bonding the core board and copper foil together.
Consequences of Low Residual Copper Rate
If the residual copper rate is too low, the overall board thickness decreases, and uneven copper distribution across layers can lead to board warping.
This is especially critical for boards with gold fingers, as their thickness must be precise to ensure a proper fit in slots. A thinner board may result in a loose fit or poor contact when inserted into the slot.
JLCPCB Recommendations
JLCPCB enginners strongly recommend :
1. For Gold Finger Multilayer Boards
Cover the blank areas with copper, especially in the inner layers near the gold finger region. This prevents issues such as the board being too thin to fit into the slot or variations in line widths.
2. For Residual Copper Rates Below 25%
To minimize uneven electroplating, which can cause inconsistent line widths and excessive board thickness deviations, add copper to the blank areas.
Common Issues in Gold Finger Design
For the golden finger areas in both the inner and outer layers, ensure that there is an open window (i.e., no solder mask bridge between each golden finger pad) to prevent frequent insertion and removal from causing ink to fall into the golden finger slot, which can result in poor contact and other functional issues.
For all types of PCBs, add copper to blank areas whenever possible, as long as it does not affect the board's performance. For boards with a residual copper rate below 25%, ensure that copper is added. In gold finger boards, copper should be applied to the inner layer near the gold finger area, and the outer layer should have a solder mask with a properly open window in the gold finger area.
Common Issues in PCB Gold Finger Design
For the golden finger areas in both the inner and outer layers, ensure that there is an open window (i.e., no solder mask bridge between each golden finger pad) to prevent frequent insertion and removal from causing ink to fall into the golden finger slot, which can result in poor contact and other functional issues.
For all types of PCBs, add copper to blank areas whenever possible, as long as it does not affect the board's performance. For boards with a residual copper rate below 25%, ensure that copper is added. In gold finger boards, copper should be applied to the inner layer near the gold finger area, and the outer layer should have a solder mask with a properly open window in the gold finger area.
Keep Learning
Understanding PCB Laminates Materials, Types, and Why They Matter
A PCB is a flat board made of a non-conductive substrate material with conductive pathways and components attached to it. One of the critical components of a PCB is the PCB laminate. A typical laminate PCB consists of a core material, such as fiberglass or composite epoxy. So what it actually do is ● Provides structural support ● Improves Signal Integrity ● Bond the layers to the core material The fiberglass layers are stacked on top of each other and pressed together with heat and pressure to create ......
Why UL94 V0 Matters for Safe and Reliable PCB Manufacturing
Key Takeaways UL94 V0 is the highest flame rating for PCB materials, requiring self-extinguishing within 10 seconds with no flaming drips. It greatly reduces fire risk and has become the de facto standard for safe, reliable PCBs in consumer, industrial, automotive, and medical applications. JLCPCB offers UL94 V0 compliant FR4 and high-Tg materials by default, ensuring regulatory compliance (UL, CE, CCC) and long-term reliability without compromising performance or budget. Never sacrifice V0 rating for......
Why Sequential Lamination Delivers Superior HDI PCBs
Did you ever ask yourself how smartphone manufacturers can crust a thousand connections into a credit card-sized board? The process is referred to as sequential lamination, which is a multi-cycle process that is used to fabricate PCBs on a layer-by-layer basis, releasing microvia structures and routing densities that cannot be accessed by a single-press process. Without it, the slick, high-performance electronics that we all use on a daily basis would not appear the way that they do now. With data rat......
PCB Material Guide : Types, Selection, and Impact on Performance
If PCB materials could talk, FR-4 would probably say, "I run 80% of the electronics industry, and still nobody appreciates me." Rogers would boast, "I'm expensive because I'm special," while Polyimide would flex literally and say, "I bend, but I don't break." The purpose of this blog is to introduce you to the types of PCB substrates available to you and how those materials affect your PCB's performance, thermal stability, signal integrity, and overall longevity. The choice of PCB material will be bas......
The Critical Role of Copper Peel Strength in Durable PCB Performance
Key Takeaways Standard Test: Measured via the IPC-TM-650 90° pull test in N/mm. Core Function: Prevents pad lifting and delamination under thermal stress and CTE mismatch. Foil Types: ED foil provides higher adhesion; RA foil yields lower signal loss. Material Benchmarks: Standard FR4 averages 1.0–1.4 N/mm, while High-Tg FR4 achieves 1.2–1.6 N/mm. Design Tips: Add teardrops, eliminate unsupported copper slivers, and perform DFM checks. Ever wonder what's making the copper stay put on your circuit boar......
Navigating Standard PCB Thickness: A Step-by-Step Guide to Selecting the Ideal Thickness for Your PCB Prototype
The thickness of a printed circuit board (PCB) may seem like a small detail, but it plays a crucial role in the performance and reliability of your electronic devices. Standard PCB thickness has become an industry norm, offering a range of benefits that impact mechanical stability, electrical performance, thermal management, and component compatibility.In this article, we will be taking a deep look at why the varying thickness of your PCB matters and provide you with a guide to choosing the right thic......