Lead Free Board Materials Reliability Phase 2
This is a follow up to the Lead Free Board Materials Reliability Project. New materials and formulations are tested to see how much improvement has been accomplished since the first project.
The Lead Free Board Materials Reliability program was started back in 2006 to evaluate the performance of printed wiring board laminate products to the increased thermal and mechanical demands of the increased surface mount reflow temperatures associated with the introduction of environmentally friendly Pb-Free solder alloys. The initial phase of the project evaluated a total of 30 material/construction combinations and found that many of the materials did perform well to the test criteria applied to replicate conditions for complex, high density, multi-layer printed circuit boards designed for high end telecommunication and IT applications.
Due to the rapid evolution of laminate systems over the last few years, largely in response to the adoption by the industry of Tin Silver Copper (SAC) soldering techniques, a significant number of new and improved products had come to the market at the start this phase of the project. Phase 2 of the project was therefore launched to evaluate this latest generation of materials while also refining the testing techniques based on the findings of phase 1.
High end PWB designs for the telecommunications and IT markets typically tend to be more complex, thicker and therefore have a much higher thermal mass than consumer products that have typically lead the way in adopting Pb-Free soldering production methods. The result of the increased thermal mass is that in trying to apply sufficient heat to enable satisfactory solder reflow of surface mounted devices, the temperature of the printed wiring board can peak at up to 260°C. Add to that the complexity of the board (typically double side assembled) and the requirement to be able to repair boards, then it is highly possible that boards throughout their manufacturing cycle could see up to 6 thermal excursions up to this 260°C level. The ability of laminate systems to withstand the combined thermal exposure without degradation or delamination and at the same time exhibiting consistent electrical properties is essential.
The aim of the project is therefore to assess the performance of selected currently available laminate products both in as fabricated test vehicles as well as after thermally conditioning the test vehicles to a total of up to 6 reflow thermal cycles. A series of tests will be applied to the test vehicles to assess the impact on reliability and electrical performance introduced by the preconditioning process.
The test vehicle used for the project is pictured below
A total of 20 different laminates were selected. For some of these constructions (marked with an *) a second higher resin construction (69% as opposed to standard 58% standard construction) was also fabricated and tested.
Conditioning of the materials was undertaken by Celestica using a standard 10 zone surface mount convection reflow oven with a standard reflow time/temperature profile peaking at 260 deg C. Each sample was run a total of 6 times through the oven.
Project process flow: