IPC 4101/99 and /124 are the Answer
For some time now the Industry has had to deal with delamination in its Lead Free Boards as it waited for a solution, which would ideally get back to processing the way we did when everything was SnPb. Delamination has occurred primarily on boards made from phenolic laminates, which are used for lead-free and high temp PCBs. While these materials have great thermal properties (Tg > 170C° and Td > 340C°, and conforming to IPC 4101/126/129), they are extremely weak in the fundamental areas of moisture absorption and copper to laminate adhesion. Moisture Absorption
Standard 130Tg FR4 materials typically have a moisture absorption rate of 0.20% when measured using a 0.028" core material. Phenolic materials often measure moisture absorption of up to 0.45% when measured using the same test vehicle. Copper to Laminate Adhesion
Standard 130Tg FR4 materials generate peel strength results of 6-9 lbs. Holding all parameters equal, phenolic materials generate peel strength results of 3-4 lbs. Vapor Escape
These material characteristics take on much more value when you consider the effects of lead-free assembly parameters. Any moisture trapped or absorbed into the PCB will escape during assembly in the form of water vapor, the force of which is measured in psi (pounds per square inch). The vapor will escape from the dielectric from the weakest point in the board, which is typically plated via holes.
During standard SnPb assembly at 200C, the vapor pressure is 225 psi. At Pb-Free assembly temperatures (250C), however, the vapor pressure increases to 575 psi. The Perfect Storm
Combining the increased vapor pressure with phenolic material characteristics of increased moisture absorption and lower adhesion strength gives you a perfect storm capable of ruining entire production runs. In fact, the forces here are so strong that often instead of just blowing vias, entire layers can separate from each other forming delamination areas of 1 square inch or greater. The Saturn Solution
Our solution is move towards non-phenolic materials, many of which can be found under IPC 4101/99 and /124. To qualify under these IPC categories for lead-free materials, they must have 150Tg and 325Td. While the thermal properties are not as high as the /126 or /129 materials, the mechanical characteristics more than make up for this, as demonstrated by lab tests we commissioned on standard test vehicles. Please see below for a summary chart. For more detailed information, please view our webinar we had on this topic at http://www.saturnelectronics.com/webinar_leadfree.htm.