Design Related PWB Material Damage

Previous results from the Pb-Free PWB materials reliability project have indicated that for the MRT test board used there is a clear relationship between design features and the increased risk of material delamination through SMT reflow. Using modified design variants of the MRT test board, this project explores further the impact of reduced through hole via pitch and hole wall to hole wall spacing, board thickness, number of layers and position of power distribution planes on the occurrence of post SMT assembly material damage.

Project stage: 
Lead company: 
Juniper

If you are interested in participating in this project:

Members - Go to the "Subscribe Here" section to the right and select the "Subscribe to space" key.

Non Members - Go to the "Contact" section to the right and select the "Contact project facilitator" key.

Idea Information

Background: 

 This project is an extension of the Pb-Free PWB Materials Reliabilty phased program. Results from earlier phases of the reliability program indicated PWBs constructed from certain materials were vulnerable to internal delamination induced by the reflow conditions at surface mount assembly. Furthermore, the delamination detected was typically more prevalent in areas where finer pitch vias were deployed. Project members also reported that in their own in-house tests they had observed different levels of delamination depending on PWB thickness, number of layers and the location of power/ground distribution planes within the layer stack.

These observations raised questions about how design choices contributed to the risk of internal material damage within PWB products.

 

Problem: 

Little information exists in the industry about the impact of PWB design on the risk of internal delamination.  Results from the HDP User Group Pb-Free PWB Materials Reliability project indicated that for the 20 layer test vehicle used, delamination was present on a number of materials tested. However it was not clear how the same materials would perform for different types of PWB design with fewer layers, and denser via spacing.  A better understanding of how certain PWB design features contribute to the risk of delamination will help designers to select the best material for the application required with greater confidence that internal board material damage will not be an issue.

Definition Information

Goals / Benefits: 
 Quantify the impact of board design on the survivability (resistance to delamination) of PWBs during Pb-Free SMT reflow processing

Scope

  • Focus on ‘hot reflow’ cycles. 260°C peak temperatures.
  • Evaluate selected materials that exhibited some delamination in phase 3 of PWB materials reliability project.
  • Use a modified version of the MRT-5 test vehicle as used in PWB materials reliability project.
High level objectives: 
  • Provide data quantifying the effect of via pitch on Pb-free survivability

  • Provide quantitative data on the effect of thickness / layers / resin content to a “lower complexity” based on materials that have already shown limitations in more complex constructions.

  • Evaluate the effect of more central plane layers in the design.

  • Further evaluate the specific materials to identify their limits.

  • Provide additional data to IPC and material suppliers to better drive requirements for material evaluation and test.

Approach: 

A modified MRT-5 test vehicle has been designed in order to:

 Quantify the effect of pitch:

  • Add 0.9, 0.7, and 0.65mm pitch IST coupons in the place of the current S-parameter section.
  • ATC  section rotated and truncated – for cross-sections and material analysis only (TMA, DMA, DSC, etc.)
  • Primary Focus on the DELAM testing

Quantify the effect of central plane layers:

  • Two “special” IST coupon designs (1mm or 0.8mm pitch) where more plane layers are added central to the design (4, and 6 planes rather than just 2 in current design)

Quantify the effect of thickness/layers in conjunction with pitch:

  • Build 12 and 16 layer versions and the 20 layer 58% Resin content construction (repeat build)
  • Use materials we already have data on at 20 layer constructions (that passed at 1mm pitch, failed at 0.8 mm pitch)
  • Quantify the effect of pitch:

The test method will use PWB Interconnect Solutions’ Dielectric Estimation Laminate Assessment Method (DELAM). The system works by measuring changes in capacitance across layers in custom designed test coupons.

 
Key Participants: 
Celestica
Ciena
Doosan / Circuit Foil
Elite Material Co. EMC
Hitachi Chemical
IBM
Isola Group
ITEQ
Juniper
Nokia
Oracle
Panasonic
PWB Interconnect Solutions
Shengyi
TTM Technologies
WUS
Public