Saturn Electronics Corporation, a Bare Board Manufacturer, took its Lead Free Cost Reduction presentation to Santa Clara, CA for the PCB West 2008 from September 14-18.  Yash Sutariya delivered the presentation, which claims that utilizing the right combination of materials, finishes, and solders can produce notable benefits, such as cutting the costs on lead free boards by up to 30% and increasing PCB reliability at the same time. 

A crowd approaching close to 40 listened in as Sutariya advanced what he felt were the main reasons for the necessary implementations of the Saturn presentation. Sutariya mentioned the direct cost drivers in the fabrication of Lead Free Boards (high-temp laminates and final finishes) before asserting that the move to Pb-free had created a host of indirect cost drivers as well, which include pre-baking, storage & handling, and an increased scrap rate due to delamination and solderability.

IPC 4101/99/124
The presentation was broken into two sections.  The first dealt with Capable Laminates for Lead Free Assembly corresponding to IPC 4101/99 and /124.  Sutariya presented numerous effects of the current state of the common callouts.  Suppliers lock customers  into laminate brand names, and typically phenolic materials that have a moisture absorption up to .45% on 0.028" core; less mechanical strength (interlaminate adhesion); more prone to delamination during assembly;  inclination to pad catering on BGA applications.  Finally, there were the non-Pb Free capable materials such as FR4.   Designers are commonly calling out FR-4 laminates with high Tg values, but without including appropriate Td callouts (time to decomposition at temperature).  While FR4 is RoHS Compliant, it is not always capable and 180° Tg does not guarantee adequate Td.

Proposed Solution
Sutariya proposed mid-grade capable Lead Free laminates compliant to IPC 4101/99 or /124 at 150 Tg min. and 325 Td min.  Utilizing this approach would lead to higher copper to laminate peel strength, higher inter-laminate adhesion, as well as lower moisture absorption.  Also, a 10-20 percent cost saving on the raw materials was promised as a result of these implementations.

The first part of the presentation ended with a promotion for the new FR406HR that is going to address the delamination during the lead free bare board manufacturing process.

SN100CL - Lead Free HASL
The second section dealt with Pb-Free HASL, specifically SN100CL and the Industry misconceptions associated with the discipline such as the predictions of HASL's inevitable demise, its solderability issues, and the short duration of its usage.

But Sutariya argued that the lower copper erosion on the PCB surface and in the vias was benefit to PCB reliability.  Other benefits included: quick process, long shelf life, lower cost, forgiving in regards to humidity, handling and temperature, and finally, Solder Joint Strength.

According to the HALT Test Results (provided by Tim Murphy of Thomson Lab Services and Glenn Sikorcin of Florida CirTech), Lead-Free HASL, with all different solderpastes pooled together, required the most energy (G-force + thermo-cycling) to break the solder joints.  Sutariya concluded that lead free HASL solder joints outperform all other surface finishes, including SnPb HASL.

Drawbacks
But there were drawbacks involved pertaining to its planar, which makes it problematic  for extremely fine pitch applications.  If you're interested in Past Solderability Issues with SN100Cl, read HASL and Flow: A Lead-Free Alternative from the February 2008 issue of CircuiTree.   Furthermore, the SN100CL requires a Thermal Cycle in addition to thermal cycles in the assembly process.

Finally, there still remains no Industry standard regarding the Thickness Acceptability Criteria for SN100CL.  As a result, smaller pads receive thicker solder deposition as a result of a Generic Thickness requirement because it is not proper to have just one solder thickness for all pad geometries.  Sutariya said the solution was to segregate the minimum alloy thickness by ranges of pad size.  By implementing alloy control, lower copper content of alloy increases solderability and the standard drossing of the solder pot is not enough to keep copper below 0.90%.

Sutariya recommended a ¼ - 1/3 solder pot dump once weekly copper content measurement reaches 0.90%.

Specific Design Set-Up
Then Saturn turned its focus to the Design link in the PCB Supply Chain and addressed the need for a specific design set-up.  In addition, adjustments would need to be made to air knife pressure, retract speed, and dwell time.  In effect, since the operating window is smaller than the SnPB, it is vital for the top of the Supply Chain to take control of the process!

Saturn and Florida CirTech have been utilizing the SN100Cl for over a year and have had no solderability issues at any customer.  He attributed this to the value of the Fab Notes that can specify the use of these coupons or range of solder thickness standards.

Sutariya concluded that by doing this, you'd take control of the process by forcing your supplier to meet these specs.

Conclusion
Saturn Electronics' Corporation's Lead Free Cost Reduction presentation concludes that through the implementation of one or both of these proposed solutions,  one can save up to 30% on their bare board costs while increasing the performance of their products.  Additionally, this makes it much easier to standardize fab notes to removable risk of non-performing products.

Sutariya opened the floor to questions from the crowd and attendees, mostly PCB Designers who had very positive feedbacks regarding the recipe Sutariya and Saturn had just shared with them. 

During this past summer, Sutariya gave the same presentation through a webinar.  Polling questions included:

Have you experienced delamination during Lead Free Assembly?
46% of attendees answered yes

Have you ever tried and subsequently abandoned SN100CL?
6% said yes
12% said no
82% had never even tried it

What is your primary Lead Free Finish?
38% said RoHS Compliant
31% said Immersion Silver
13% said ENIG
13% said Lead Free HASL
6% answered Immersion Tin

PCB West is for PCB engineers, designers, fabricators and managers and includes a five-day conference of more than 35 technical courses.

Saturn Electronics Corporation is a leading manufacturer of high-reliability, and technologically advanced printed circuit boards. Dedicated to quality since our inception, Saturn delivers steadfast manufacturing that ranges from quick-turning elaborate prototypes to scheduled principal volume-production.

Saturn's adherence to quality resulted in being the first PCB Manufacturer in North America to achieve TS16949certification.

To view the archived version of this presentation, please email jim@saturnelectronics.com