Introduction
Acid traps have been a challenge in PCB production since they generate multiple risks that affect both board reliability and operational life span. While there are reduced usage of acid traps because of to improvements in design software, some manufacturing techniques still can generate problems because of acid traps.
What is an Acid Trap?
Acid traps occur when a pad and a trace are positioned too closely to each other. These small gaps create areas where etching acid can accumulate during the PCB manufacturing process. As the acid lingers in these spots, it can gradually erode the copper traces. This corrosion can result in open circuits, shorts, or weak connections that might lead to board failure over time. While they may not always impact functionality, acid traps complicate the etching process and can leave undesirable marks on the PCB surface.
Acid TrapPCB Etching
Etching is the method used to eliminate excess copper from the PCB to create the desired circuit pattern. Traditionally, chemical etching requires submerging the PCB in an acid solution that dissolves the unprotected copper. However, if certain design elements unintentionally create areas where acid can collect, the solution might not rinse away completely, resulting in weak spots that can deteriorate over time. Although advancements in etching methods, like spray etching and dry etching, have reduced some risks, acid traps can still pose a threat if the layout isn’t properly optimized.
PCB EtchingCause of Acid Traps
Acid traps form when small gaps catch etching acid. The acid sits in these spaces and corrodes the copper traces. Here are the common causes of acid traps:
Traces That Meet at Acute Angles
Sharp angles in traces create areas where acid can accumulate. Any angle less than 90 degrees heightens this risk. The acid that gets trapped can gradually corrode the copper, weakening the connection and potentially leading to circuit failures. Even a right-angle trace can present problems over time. These angles are often easy to miss, even for seasoned designers. When two traces intersect, small sharp corners may develop.
Minimal Gaps Between Pads, Traces and Vias
When gaps are too small, acid can become trapped. It accumulates in these narrow spaces and gradually erodes the copper. This can lead to corrosion, weak connections, or even short circuits. Thin traces are particularly at risk since there’s less copper available to wear away. If the acid reaches the vias, it can move to the opposite side, potentially causing damage on both sides of the PCB. Even if the board functions well initially, these hidden issues might surface later on.
Isolated Copper Islands
Copper islands are small, isolated spots that are left behind after the etching process. Although they don’t serve any function, they can cause problems. Acid can build up in these areas and become trapped. Over time, it may leak out and corrode nearby traces. This can weaken solder joints and lead to connection failures. While they might seem innocuous, these islands can make the board unreliable. Thankfully, many design tools can automatically remove them, so it’s important to look for their presence.
System Errors
Automated design software can greatly speed up the PCB layout process. However, it can also unintentionally create acid traps. Small gaps and sharp angles might be overlooked. If the settings aren’t configured correctly, these issues can appear in the final design. Even with design rule checks, some errors may still go unnoticed. It’s crucial to carefully review the layout before proceeding to manufacturing. A small acid trap now could result in significant problems later on.
Cause of Acid TrapsWhat Issues Can Acid Traps Cause to Your PCB?
Copper Trace Corrosion
Acid traps can corrode copper traces, weakening connections and potentially leading to open circuits. If a trace deteriorates significantly, signals may not transmit correctly. Over time, this can result in device failure or short circuits.
Acid Seepage into Vias
Acid can infiltrate open vias, causing further damage. It might even reach the opposite side of the PCB, affecting inner layers in multilayer designs. If not addressed, this can lead to hidden failures over time.
Erosion of Solder Pads
Solder pads are small copper areas designated for connecting components. If acid reaches these pads, it can erode them. Without intact pads, proper component attachment becomes impossible, rendering the PCB unusable, even if all other parts function correctly.
Damage to the Solder Mask
The soldermask serves to protect copper traces from oxidation. Exposure to acid can compromise this protective layer, leaving the board vulnerable to rust and short circuits. Over time, this can reduce the PCB’s lifespan and impact its performance.
PCB CorrosionHow to Improve the Manufacturing Process if You Experience Acid Traps?
Dealing with acid traps can be frustrating. Luckily, there are ways to improve the manufacturing process and avoid these issues. Here are some tips you can follow.
Proper Photoresist Process
A successful photoresist process begins with a uniform coating. Manufacturers must first apply photoresist to the copper surface. Following that, a dry film containing the trace layout should be applied. When this resist is exposed to UV light, it hardens, safeguarding the traces during the etching process.
Proper Dry Etching
Using dry etching significantly improves precision. This technique utilizes plasma gases such as fluorocarbons and oxygen. It effectively removes excess metal, resulting in superior outcomes compared to traditional methods. This approach is an excellent way to achieve cleaner and more accurate PCB designs.
Ensuring Precision
High-quality fabrication methods provide improved control. Even without the use of photoresist, manufacturers can efficiently remove excess etching solution. This guarantees that your PCB features accurate traces and clean edges, ultimately boosting its overall quality and performance.
Drilling Holes with Extra Vias
Adding extra vias can help avoid acid traps. If you spot a potential issue, think about drilling some additional holes. This will enable acid to drain away from crucial traces and components. Just be cautious not to harm any important parts while drilling.
Use Photoactivated Etchants
Photoactivated etchants can also be used. They lower the chances of acid traps and are more user-friendly. In contrast to conventional chemicals, these etchants activate solely under UV light, which helps to limit damage to areas on your board that you don’t want to affect.
Run DRC
Running a Design Rule Check (DRC) is crucial. This software assists in spotting layout problems before you submit your design. It verifies that traces comply with width specifications and confirms that all components are properly spaced. Conducting a DRC can help you avoid expensive errors down the line.
Run DFM
Design for Manufacturing (DFM) software like Autodesk Fusion 360, Siemens NX, and SolidWorks improves the manufacturability of your PCB. It helps identify potential acid trap issues and optimizes your design. By using DFM, you make it easier for manufacturers to produce high-quality boards more efficiently.
Is 90 Degree Angles Automatically Are PCB Acid Traps?
You may have heard that 90-degree angles in PCB design are not recommended. While this was true in the past, things have changed. Previously, PCB etching used acid, which could trap harmful chemicals in sharp corners. Today, many PCB manufacturers have switched to alkaline etching, which greatly minimizes the risk of chemical entrapment. Additionally, modern techniques are more effective at rinsing away any leftover residue.
To avoid acid traps, it’s best to steer clear of sharp angles in PCB designs. Right-angle traces can retain corrosive substances, and acute angles are even more problematic. Opting for 45° angles or curved traces can help minimize this risk. For T-junctions, incorporating teardrops or slashes is beneficial. Ensuring that traces are smooth and well-connected leads to stronger, more reliable circuits.
90 Degree Angle in PCBHow We Handle Acid Traps at PCBMay
At PCBMay, we implement advanced design validation processes, including DRC and DFM checks, to avoid acid traps before production starts. We have etching technology ensures complete copper removal, reducing the risks associated with acid retention. We maintain strict quality control standards and working closely with customers on optimal PCB layouts, and we deliver reliable and long-lasting circuit boards.
Conclusion
Acid traps can threaten the reliability of PCBs, but with proper design and manufacturing practices, these issues can be mitigated. Ensuring sufficient spacing and utilizing advanced etching techniques can help minimize these risks. If you’re in need of high-quality, defect-free PCBs, contact PCBMay today for tailored manufacturing solutions that meet your specific requirements.
