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Lead Free Board Materials Reliability 3

Idea/Definition Information
Summary: 

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 looks at recently released materials and focuses on laminates designed for high speed applications. The project will submit 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. 

If you are interested in this project and would like to subscribe to the project mailing list, please click here (members only) or email the project facilitator, Brian Smith - brians@hdpug.org.
 

Background: 

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. To date two rounds of evaluations have been completed and a total of 43 different laminates have been assessed.

This 3rd phase of the program targets laminates that have recently been released and specifically focuses on those materials with high speed and /or halogen free properties.

Problem: 

Over the past few years the PWB industry has seen the development 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 will therefore identify a range of high speed materials and submit them to the same test program developed and perfected throughout phase 1 and 2 of the project.


 

Approach: 

The project will adopt the same approach as used in phase 2.

A list of laminate products to be tested will be agreed by the project team.  A test vehicle with minor modifications to that used in phase 2 (see below) will be used.

 

Boards will be fabricated under controlled conditions. Laminate suppliers will be consulted to ensure that their recommendations are followed  for lamination and processing of their materials.

The completed boards will be preconditioned using a typical high end surface mount reflow cycle peaking at a maximum temperature of 260°C. The boards will be passed through the convection oven a total of 6 times, being visually inspected and allowed to cool to ambient after each cycle.

The boards will be then be submitted to a series of tests as defined below.