Plating Bath Metallic Dopant Dosing for Kirkendall Void Suppression
Dosing electroplating copper baths with controlled nickel or manganese trace dopants suppresses Kirkendall void accumulation and preserves joint shear strength.
Microvia Plating Defects
Meaning
Structural imperfections in the copper walls of small diameter vertical interconnect accesses occur when the plating chemistry fails to reach the bottom of the hole. These microvia plating defects are a common problem in the manufacturing of high density interconnect circuit boards, which are used in smartphones and other compact devices. The defects can include voids, where the copper is missing entirely, or thin spots that can break under thermal stress.
In China, where a large portion of the world’s consumer electronics are produced, managing these defects is a primary focus for PCB quality control teams. The boundary of the issue is the physical space within the microvia and the interface with the copper pad at the bottom.
Geometric Origins
The small size and high aspect ratio of modern microvias make them very difficult to plate correctly. When microvia plating defects occur, it is often because the liquid in the plating bath was unable to circulate freely inside the hole. This can lead to a build up of air bubbles or a depletion of the copper ions at the bottom of the via.
If the hole is not properly cleaned after the laser drilling process, any remaining debris can also prevent the copper from adhering to the walls. As the industry moves toward even smaller features, the challenges of plating become even greater. Engineers must design the holes carefully to ensure they can be manufactured reliably.
This involves finding the right balance between the diameter of the hole and its depth.
Remediation Steps
Preventing defects in the plating process requires a combination of high quality equipment and careful chemical management. To avoid microvia plating defects, manufacturers use advanced vacuum systems to pull the air out of the holes and ensure that the plating solution reaches every surface. They also use specialized vibrators and ultrasonic cleaners to remove any debris from the drilling process.
The chemistry of the plating bath is another important factor, as certain additives can help to improve the flow of the solution into the small features. Regular maintenance of the bath and the use of filtered solutions help to keep the level of contaminants to a minimum. If a defect is found, the engineering team must identify the cause and take corrective action, such as adjusting the current density or the plating time.
This constant monitoring is necessary to keep the production line running smoothly.
Reliability Impact
The presence of even a tiny defect in a microvia can have a major impact on the long term performance of an electronic device. These microvia plating defects can act as points of high stress that can lead to the formation of cracks as the board heats up and cools down during use. Over time, these cracks can grow until the electrical connection is lost entirely, causing the device to fail.
Because these components are often used in critical applications such as mobile communications and medical devices, the reliability of the connections is of the utmost importance. Quality control teams use thermal cycling tests and electrical measurements to verify that the microvias are robust enough to withstand the demands of the real world. A failure in these tests can lead to the rejection of an entire batch of boards.
This attention to detail is what allows Chinese manufacturers to produce some of the most advanced electronics in the world. By continuously improving their processes, they can stay ahead of the competition and meet the needs of their global customers.