Reading time ( words)
Joemar D. Apolinario, manufacturing engineering manager, and Dnichols R. Dulang, process engineer at EMS firm Integrated Micro-Electronics Inc. discuss with SMT Magazine the impact of plating and surface finishes on electronics assemblies. They highlight the impact on solderability, the problems with complex components and packages, as well as parameters to consider when it comes to surface finish selection.
Stephen Las Marias: From your perspective, what are the greatest challenges when it comes to plating and surface finishing?
Joemar Apolinario: The greatest challenges that we face include obtaining good connectivity between the PCB and the component, and having good solder joint reliability; proper selection of the surface finish that will satisfy the product application requirements, cost, reliability and compliance to ROHS; proper handling and storage; and signature defects such as visual cosmetics (exposed copper), plating thickness integrity (especially high-value materials such as silver and gold) from the PCB manufacturer.
Dnichols Dulang: The greatest challenges are the problems due to visual cosmetics and solderability, both for TH and SMT pad surfaces.
Las Marias: What are the most common plating and/or surface finishing defects?
Apolinario: Common defects include discoloration (oxidized pad), corrosion, contamination, and exposed copper. These PCB defects normally results in solderability problems, and affect product reliability.
Dulang: Other defects are de-wetting, black pad defect, and tin/silver whiskers.
Las Marias: How do surface finishes affect your assembly process?
Apolinario: If the surface finish is not properly determined based on the product component and application, it will impact solderability. Solder wetting is not good for the oxidized pad. Some characteristics of various surface finish are not compatible with some components like fine pitch ICs due to planarity issues. Some finishes, such as OSP, also require extra sensitivity in handling. One critical point is that we should understand how we handle the different surface finish, so that we can put appropriate controls and parameters that will fit the product applications.
Las Marias: What about plating? How does plating affect your assembly process?
Dulang: Plating is one of the critical parameters. If plating does not comply with the specifications, then there is a strong possibility to encounter assembly problems. Plating can cause functional test failures due to connectivity issues. The worst reliability failure is the intermittent failure due to cracks. Compatibility of surface plating to solder paste and component plating are very critical points.
Las Marias: Are there parameters to consider when it comes to plating and/or surface finishing that will help optimize your assembly process?
Apolinario: The parameters are the right selection of surface finish, then PCB pad cleanliness. Plating thickness should be considered to optimize the assembly process and testing, as well as handling and shelf life.
To read this entire article, which appeared in the January 2017 issue of SMT Magazine, click here.