Solder balls can be caused by a variety of factors, making a diagnosis of the problem somewhat challenging. In some cases, they can be completely random. Here are a few of the common reasons solder balls form in the Health care PCB assembly process.

Humidity – Moisture has increasingly become one of the biggest issues for printed circuit board manufacturers today. Aside from the popcorn effect and microscopic cracking, it can also cause solder balls to form due to escaping air or water. Ensure that printed circuit boards are dried properly before the application of solder, or make changes to control humidity in the manufacturing environment.

Solder Paste – Problems in the solder paste itself can contribute to the formation of solder balling. Thus, it is not advised to re-use solder paste or allow the usage of solder paste past its expiration date. Solder paste must also be properly stored and handled per the guidelines of a manufacturer. Water soluble solder paste can also contribute to excess moisture.

Stencil Design – Solder balling can occur when a stencil has been improperly cleaned, or when the stencil has been misprinted. Thus, trusting an experienced printed circuit board fabrication and assembly house can help you avoid these mistakes.

Reflow Temperature Profile – A flex solvent needs to evaporate at the correct rate. A high ramp-up or pre-heat rate can lead to the formation of solder balling. To resolve this, ensure that your ramp-up is less than 1.5°C/sec from average room temperature to 150°C.