If you’re a manager, procurement engineer, or production lead in industrial electronics, automation equipment, or IoT hardware, you know even small PCB defects can lead to big problems. Solder joint voids—tiny air pockets trapped in solder connections—are one of the most common yet overlooked issues in PCBA manufacturing.
Here’s a startling statistic: 20% of PCBA failures are linked to solder joint voids. These small cavities might seem insignificant, but they can weaken your products, cause short circuits, and damage your reputation with clients.
Figure 1PCBA failures
In this guide, we break down the hidden dangers of solder joint voids, their acceptance standards (per IPC guidelines), the key causes behind them, and how to prevent them—so you can deliver reliable, long-lasting PCBA and avoid costly rework or returns.
The Two Critical Dangers of Solder Joint Voids
Solder joint voids aren’t just a cosmetic issue—they directly compromise the performance and reliability of your PCBA. Here are the two main risks you need to watch for:
1. Reduced Welding Strength & Reliability
Voids shrink the effective welding area of the solder joint, weakening its mechanical strength. Over time, this makes the joint more prone to cracking or failure—especially in industrial equipment that undergoes vibration, temperature changes, or long-term use.
2. Short Circuits Between Solder Joints
As voids form, they can push molten solder outward. This excess solder may bridge adjacent solder joints or components, creating short circuits that cause immediate functional failures or intermittent issues that are hard to diagnose.
Solder Joint Void Acceptance Standards
Voids can be observed using cross-sectioning or X-ray inspection—with X-ray being the most common and reliable method for judgment, especially for BGA (Ball Grid Array) solder balls. Below are the key industry standards (per IPC guidelines) you need to follow:
From a top-down view (via X-ray), the area of a void must not exceed 25% of the total solder ball area. This is the most widely referenced standard for BGA solder joint voids in industrial PCBA manufacturing.
Figure 2Top-down view via X-ray
This standard provides more detailed definitions for BGA solder joint void acceptance, including guidelines for void distribution, size limits for multiple voids, and exceptions for specific component types—critical for high-reliability applications like automotive or medical PCBA.
The Mechanism Behind Solder Joint Void Formation
In simple terms, solder joint voids form when gas is generated during the solder melting process and gets trapped in the molten solder. The gas can come from several sources, which we’ll break down next.
Key Causes of Solder Joint Voids
Understanding the root causes of voids is the first step to preventing them. Below are the most common culprits in SMT and wave soldering processes:
Flux residues that aren’t expelled from molten solder can crack under high temperatures, forming voids. High-activity flux helps prevent this by accelerating wetting, reducing the chance of flux residues being trapped in the solder.
2. Moisture Absorption & Oxidation of Three Key Components
The “three components”—component leads, solder paste, and PCB pads—are frequent sources of void-causing gas:
3. PCB Pad Design Issues (Vias on Pads)
During SMT, when solder covers vias on PCB pads, air inside the vias is difficult to escape—trapping gas and forming voids. Per the J-STD-001D standard, these voids are acceptable if they don’t exceed 25% of the solder area.
4. PTH Hole Breakage (Wave Soldering)
Plated Through-Hole (PTH) breakage—often caused by drilling or copper plating issues—allows moisture and chemicals to seep into the PCB during wet manufacturing processes. When heated during wave soldering, these substances release large amounts of gas, creating “blow holes.”
5. Inadequate PCB Surface Finish
Poor anti-oxidation surface finishes lead to more voids. For example:
OSP (Organic Solderability Preservative) finishes can crack under heat, generating gas.Bare copper pads oxidize easily, producing large amounts of gas during soldering.
6. Improper Reflow Time
Reflow time directly impacts void formation:
A slightly longer reflow time helps gas escape, reducing voids.Excessively long reflow time accelerates flux cracking and pad re-oxidation—creating more voids.7. Kirkendall EffectThis long-term issue occurs when tiny holes in the solder joint’s Intermetallic Compound (IMC) layer grow larger over time, eventually forming cracks or large voids that cause joint failure. It’s caused by unequal atomic diffusion:
FIgure 3Improper Reflow Time
How to Prevent the Kirkendall Effect
Two effective strategies to avoid Kirkendall-related voids:
Add a nickel (Ni) barrier layer to copper pads: Ni diffuses much slower in solder than Cu, stopping atomic diffusion after soldering.Add a small amount of copper to the solder paste: This inhibits Cu diffusion from the pad into the solder, preventing void formation.Conclusion: Prevent Voids to Protect Your PCBA Quality Solder joint voids are common, but they’re not inevitable. By addressing the root causes—from using high-activity flux and proper PCB surface finishes to optimizing reflow profiles and preventing moisture absorption—you can significantly reduce voids and improve PCBA reliability.
Figure 4Kirkendall Effect
At Fumax, we specialize in tailored PCBA solutions for industrial, automation, and IoT customers. Our engineering team optimizes every step of the manufacturing process—from solder paste selection to X-ray inspection—to eliminate voids and deliver defect-free PCBA, whether you need prototype, small-batch, or high-volume production.
Tired of costly PCBA failures caused by solder voids? Contact us today to learn how our SMT assembly services can streamline your production and boost your bottom line.
