Solder Balls on a PCB

Solder Balls on a PCB

Solder is necessary for connecting components to an electrical circuit board, though it can also be a significant area for potential problems. Solder balls are one of the most common issues experienced with printed circuit boards (PCBs), making them important to understand and prevent. Solder balls form for many reasons depending on the material and technology used. Understanding the potential causes of solder balls on PCB helps you know what to look for and how to prevent them in your circuit boards.

Learn more about solder balls and what they can do to your PCBs.

What Is a Solder Ball?

Solder is used to permanently bond metal, creating strong electrical joints. The soldering process involves heating a metal alloy like tin, copper, brass or silver beyond its melting point. Once the alloy is melted, it’s applied to a circuit board where it cools to create soldered joints. For example, chip packages are connected to a PCB via soldering. Unfortunately, soldering can cause defects when manufacturing PCBs. Solder balls are one of the most common defects and are a primary concern when assembling surface mount technology.

Solder balls are hard to control because numerous factors can cause them to form. For example, solder can get squeezed underneath the inside of the pad, then the reflow process separates that solder from the main mass, forming its own solder ball. Solder balls are mainly found on the side of chip components, though they are also commonly found around the pins of connectors and integrated circuits (ICs).

What Causes Solder Balls?

In many cases, the cause of solder balls is a result of flaws in the PCB assembly process. The most common causes of solder balls can be categorized into material and technological causes. Consider some of these causes of solder balls:

Material Causes

Four materials used in the PCB process can cause solder balls — solder paste, pads, stencils and the scraping blade. Here’s a closer look at each of these materials and how they can cause solder balls:

  • Solder paste: Solder paste can cause solder balls when there’s low activity temperature, excess flux, uneven metal particles, oxidized tin powder, humidity absorbed in the paste and cold or slightly thermal collapses.
  • Pads: The PCB pads themselves can cause solder balls if the components have low solderability or there are small spaces between the pads.
  • Stencils: If the stencils used during the PCB assembly process have burrs on the opening wall, solder balls are more likely to occur. A dirty stencil also tends to cause solder balls.
  • Scraping blade: A lightweight or distorted scraping blade can also cause solder balls to form.

Technological Causes

Technological causes of solder balls have more to do with the processes used to assemble PCB than the materials used. For example, solder balls are likely to occur when:

  • The mounting pressure is too high.
  • The solder paste is applied improperly.
  • Paste residue collects between the pad and stencil.
  • There is too much space between the stencil and PCB.
  • The soldering temperature is set too high or low.

Solder balls can form based on numerous other factors related to the staff, environment and equipment used to assemble PCB.

What Can Happen if Your PCB Has a Solder Ball?

While solder is a crucial element of assembling PCB, solder balls are a negative defect that can jeopardize your circuit, resulting in a significant waste of time, money and resources. At the very least, solder balls will affect the appearance of your electronic products. Excess solder balls are visible, making them visually less appealing to buyers.

More seriously, solder balls will negatively impact the reliability of the PCB’s electric capabilities. If the solder balls surpass the electrical clearance minimum, your PCB will be more likely to fail and will be unreliable during electrical use. Additionally, solder balls can fall off and cause shorts in the circuit board. Shorts in your PCB can cause damage to any other electrical components connected to the board, causing the entire circuit to fail.

How to Prevent Solder Balls

How to Prevent Solder Balls

With so many potential causes of solder balls, they’re almost inevitable. The best way to eliminate them is to take preventive measures during your assembly process. Proper storage of PCBs, preparation, clean equipment and suitable materials can go a long way in preventing solder balls from forming.

  • Store PCB in dry environments: Excess moisture and humidity in and around the circuit boards can cause solder balls to form. To help prevent moisture from reaching the PCBs, be sure to store them in a dry environment. Appropriate storage prevents damage from occurring before use.
  • Dry and preheat the board before printing: Before you print your board or make any connections, properly dry and preheat your PCB. Taking this step helps evaporate any traces of water or moisture that may have collected in or on your circuit boards.
  • Clean stencils before use: Another simple step you can take to prevent solder balls is cleaning the stencils before applying your solder paste. A clean stencil ensures there is no residue from previous uses that could affect the application of the paste.
  • Properly apply flux: Applying flux in suitable amounts helps prevent excess air and water from getting trapped. Flux should also be properly evaporated before applying the solder paste. To ensure you apply flux correctly, you may need to adjust the PCB preheating temperature.
  • Consider pad size and space requirements: Depending on your PCB, you will have different pad space and size requirements. Adhering to these requirements helps prevent abnormal results during board printing.
  • Use a compatible solder paste: The paste you choose can directly affect the soldering quality on your PCBs. Use a solder paste that is compatible with the pad in terms of oxidation, metal content, metal particle size and paste thickness. Compatible pastes will help reduce the likelihood of solder balls forming.

Learn More About PCBs With Millenium Circuits Limited

You may face various issues when working with PCBs, and they can fail for numerous other reasons. Whether you’re experienced with PCB electrical components and issues or are experiencing your first PCB failure, Millenium Circuits has the resources to help you troubleshoot your PCBs. We’re committed to partnerships with our customers and work as a strategic partner to offer quality PCB solutions. With over 15 years of focused experience, MLC has the expertise to help you with your unique needs.

Contact us with any questions or for more information about PCBs.

Learn More About PCBs With Millenium Circuits Limited