PCB Materials

PCB materials covers more than just lead free finishes. Making the transition to lead free soldering alone can lead to damage and reduced reliability of the base materials used to manufacture the board.

Laminate

Manufacturers must work with their laminate suppliers to ensure they will be providing materials that will be able to withstand multiple reflows at higher processing temperatures. Two concerns with higher soldering temperatures are the z-axis expansion and decomposition of the laminate.

Higher soldering temperatures result in higher levels of z-axis expansion, which may affect PTH reliability. Laminate suppliers will be able to provide the correct Tg for the material to prevent the z-axis expansion.

Decomposition, or breaking of polymeric bonds, happens during high-temperature soldering. Although tests are conducted regularly for laminate, which calls for the materials to survive a steady 288° C temperature for 15 to 20 minutes, mere seconds during a soldering operation could break polymeric bonds within the material.

Although the polymeric bonds broken will most likely be a very small percentage (i.e., 3 to 5 percent), one should consider this from a reliability standpoint the same as breaking a few cables on a suspension bridge. The results of small bond breakage could lead to moisture inclusions and even poor Tg.

Aside from those issues and warpage of the PCB, higher reflow temperatures will also affect inks adhesives and markings.

Available Finishes

Because it is important to protect the copper conductors on PCBs from degradation, PCBs are applied with finishes via hot air solder leveling (HASL), electroless metals, and organic solderability protectants (OSPs). Because a fully lead free electronic assembly will call for there to be no lead in the finish, board fabricators must select an alternative rated on cost, reliability, and shelf life.

In conjunction with the U.S. Environmental Protection Agency (U.S. EPA), IPC conducted an evaluation of  alternative solder finishes.  EPA, IPC and EIA are currently conducting a life cycle assesment and lead free solders.