Lead Free Board Materials Reliability 3
This project is the third phase of an initiative originally started in 2006 to assess the performance of latest generation (at the time) PWB laminate systems after being exposed to simulated Pb-Free surface mount soldering conditions. The third phase looked at recently released materials and focused on laminates designed for high speed applications. The project submited selected laminate systems to an extensive mechanical and electrical integrity testing program to verify whether the materials are prone to deterioration during higher temperature soldering conditions.
The Pb-Free PWB Materials Reliability program was commenced in 2006 in response to requests from several HDP User Group members to conduct an extensive evaluation on a range of recently launched laminate materials designed to be compatible with Pb-Free soldering processes in printed circuit board assembly. The aim was to evaluate the different materials using a range of testing techniques. A common test vehicle was designed to enable direct comparison of performance. Two rounds of evaluations have previously been completed and a total of 43 different laminates have been assessed.
This 3rd phase of the program targeted laminates that have recently been released and specifically focuses on those materials with high speed and /or halogen free properties.
Over the past few years the PWB industry has seen the development of a new family of laminate systems to address the increasing physical demands of withstanding Pb-free soldering processes used in the assembly of RoHS compliant products. Many of the materials launched as Pb-Free compatible have been found to perform perfectly satisfactorily for consumer type products where reflow temperatures peak around 245°C. However for many high end and high reliability PWBs, where the designs are complex with high layer counts and densely populated components, the thermal mass associated with these products results in the board surface seeing reflow temperatures up to 260°C. Adding to this the requirement for multiple reflows, the possibility for cumulative physical damage to the laminate is increased significantly. In previous phases of this project it was found that, many laminate materials, preconditioned by passing them through a surface mount convection reflow oven peaking at 260°C for a total of 6 cycles, exhibited significant physical and electrical degradation making them unsuitable for use in high reliability applications. While resin formulations have improved significantly since phase 1, testing of new materials is still necessary to ensure that they meet the specific requirements of high end designs.
This project therefore identified a range of high speed materials and submited them to the same test program developed and perfected throughout phase 1 and 2 of the project.
Assess the impact of the Pb-Free soldering process on latest generation of PWB laminates.
Focus on suitability for high layer count / high thermal mass board design applications in which board surface could see temperatures up to 260° C peak reflow temperature.
Fine tune the testing process between consecutive phases
Select recently launched or about to be launched materials
The project will adopted a similar approach to that used in phase 2.
A list of laminate products to be tested was agreed by the project team.
- ITEQ IT-180i
- Isola IS185HR
- Shengyi S-1190 - fabricated by TTM/Meadville
- EMC EM-370(D)
- Shengyi S1165
- Ventec VT-447
- EMC EM-828
- ITEQ IT-170GRA
- Panasonic R1577(Megtron 2)
- TUC TU-872SLK
- ITEQ IT-200LK
- Shengyi S7038
- Nelco D6000-2
A test vehicle with minor modifications to that used in phase 2 (see below) was used.
Boards were fabricated under controlled conditions. Laminate suppliers were consulted to ensure that their process recommendations were followed for lamination and handling of their materials.
Half the completed test boards were preconditioned using a typical high end surface mount reflow cycle peaking at a maximum temperature of 260°C. The boards were passed through the convection oven a total of 6 times, being visually inspected and allowed to cool to ambient after each cycle.
The boards were then be submitted to a series of tests as defined below.