Lead Free PWB Materials Reliability Phase 5
Phase 5 of the Lead-Free PWB materials reliability program will evaluate selected latest generation PWB laminates. The testing program will include thermal analysis and stress testing, thermal cycling endurance, susceptibility to CAF and evaluation of electrical characteristics at high frequencies using a new connectorless SPP (short pulse propagation) design. Properties will be evaluated both before and after multiple simulated reflow conditions.
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The first phase of the LF PWB materials reliability project was launched in 2006 in response to the introduction of the ROHS directive in Europe. While system integrators were granted exemptions on many of their high reliability products, concerns existed that the higher Pb-free reflow temperatures needed to solder non-consumer, larger, high layer and densely populated printed circuit boards could cause thermal damage and de-lamination within the board materials. Initiated by several of the organization's OEM members, the project team selected several different laminates from various suppliers and tested them before and after conditioning them, using a reflow profile peaking at 260 deg C, significantly higher than the 245 deg. C typically used by vendors to qualify their materials. In order to simulate real manufacturing and rework conditions each test board was submitted to 6 reflow cycles. The results from phase 1 indicated that significant damage was seen on many of the laminates studied, much of which was not apparent from visual inspection but could potentially lead to latent defects in the field. Since phase 1 , 2 further phases of testing have been competed, targeting materials recently released at the time of the testing. To date, a total of 56 different materials have been tested with later released products exhibiting much improved results but with several still indicating that they can not completely withstand the 6 x reflow cycles.
Since initiating phase 3 of this test program a large range of new laminate systems have been developed and released to the market. As with previous materials, qualification programs conducted elsewhere on these products have typically been undertaken using lower SMT reflow temperatures than would typically be needed for manufacture of high end, high complexity printed circuits boards. Concern still exists among HDP members about the robustness of these new materials. The project therefore sets out to test them using similar criteria to that used in the previous phases of this project.
The project has one primary goal:
To evaluate a selection of latest generation high speed laminate materials to determine their suitability for high layer count and large area printed circuit boards used for high reliability applications.
The project focus will be on mechanical and electrical reliability of the chosen materials when exposed to higher end Pb-Free surface mount reflow temperatures typical of the conditions needed to assemble large, thick and high complexity printed circuit board designs. Test vehicles will be built using Nokia'a MRT-6 design