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ROMULUS, MI – The right combination of materials, finishes and solders can have a marked effect on bare board cost and reliability.
 
Indeed, according to Jim Kelch, director of sales/marketing, at PWB fabricator Saturn Electronics Corp., the right recipe can cut board costs as much as 30%.
 
In a Webinar Monday, Kelch, along with representatives from Isola Group and Florida CirTech, laid out how.
 
The move to Pb-free creates a host of indirect cost drivers, said Kelch, including increased scrap rate (due to delamination and decreased solderability) and the need for additional storage and handling steps (generally, pre-baking).
 
The response, according to Kelch, is designers are calling out FR-4 laminates with 180° Tg and 340° Td (time to decomposition at temperature).  But while FR-4 is RoHS compliant, it is not always right for Pb-free assembly, he explained, while 180° Tg does not guarantee adequate Td.
 
Saturn’s proposed solution: mid-grade Pb-free capable laminates that meet IPC-4101/99 (filled) or IPC-4101/124 (unfilled), with a minimum 150° Tg and 325° Td.
 
The benefits, he says, are a 15 to 20% cost savings on raw materials; lower moisture absorption (0.10 to 0.25%); higher interlaminate adhesion (peel strength = T-288 >10 min.), and high copper-to-laminate peel strength.
 
Dave Coppens, technical account manager at laminate supplier Isola, discussed test results for the company’s IS400 product, which reportedly performed well under tests for TGA, DSC, Td, weight loss % by TGA, peel strength and 6X reflow.
 
Next, Glenn Sikorcin, sales manager at Florida CirTech, which is one of the North American licensees for Nihon Superior’s SN100CL, an all-tin solder alloy, shared results of Pb-free HASL and HALT tests. Pb-free HASL required the most energy (G-force and thermal cycling) to break solder joints, and outperformed SnPb HASL in the tests, according Sikorcin. He noted Pb-free HASL (also called HAL) has certain drawbacks, including a non-planar finish, and it’s not ideal for extremely fine-pitch applications; there are post-solderability issues, and SN100CL requires a thermal cycle in addition to thermal cycle in assembly. Finally, no industry standards exist for Pb-free HASL.
 
Based on Isola and Florida CirTech’s studies, Kelch said, “By implementing one or both solutions, you save up to 30% of bare board cost; increase product performance; standardize fab notes to remove risk of non-performing products, and improve your supply base.”
  
During the Webinar, Kelch took audience polls. Here are some results:
 
Have you experienced delamination during Pb-free assembly?
–        Yes 46%
–        No 54%
 
What is your current lead-free finish?
–        ENIG: 32%
–        Pb-free HASL: 32%
–        Immersion silver: 15%
–        Immersion tin: 0%
–        RoHS compliant: 21%