Activate your solderability testing program: a summary of the decision to use ROL1 flux for solderability testing standards.

This month brings the publication of long-awaited updates to two of the electronic industry's solderability test methods. IPC/EIA/JEDEC J-STD-002B, Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires, and IPC/EIA J-STD-003A, Solderability Test for Printed Boards, present the results of more than three years of research to assure test results provide meaningful data.

One of the most extensive changes implemented involved the flux used in solderability test methods. The clause in each standard defining the required flux reads: "The flux for all solderability tests shall be a standard activated rosin flux (Type ROL1 per J-STD-004, Requirements for Soldering Fluxes) having a composition of 25% [+ or -] 0.5% by weight of colophony and 0.15% [+ or -] 0.01% by weight diethyl-ammonium hydrochloride (CAS 660-68-4), in 74.85% [+ or -] 0.5% by weight of isopropyl alcohol. The specific gravity of the standard activated rosin flux shall be 0.843 [+ or -] 0.005 at 25 [+ or -] 2C."

The Joint IPC/EIA/JEDEC working group leaders understood that any proposed change to the use of ROL0 (formerly designated type R) would be heavily scrutinized and would require test data showing the applicability of using a standard activated flux composition. Members of the joint working group have spent the last two years evaluating this flux change issue, discussing the chemistry details and conducting multi-company design of experiment investigations. The committee has compiled a significant data set and held thorough topic discussions supporting the proposed flux material change.

A Proactive Approach

A number of industry studies, such as the 1996 NEMI Surface Finishes Task Group Report, the 1997 NCMS Lead-Free Solder Project and the 2000 National Physical Laboratory CMMT (A) 284 Report, have shown an incompatibility of "R type" flux with non-tin surface finishes, such as palladium, organic solderability preservatives (OSPs) and immersion gold. The introduction and use of these surface finishes on components and printed wiring boards (PWBs) is no longer the exception, but is quickly becoming the norm. The use of an R type flux containing only naturally occurring activators has resulted in false negative solderability test results, which negatively impact both the component/board fabricator and the assembler in terms of cost and schedule.

Reduced Solderability Test Variability

Dr. Carol Handwerker and resources of the National Institute of Standards and Technology (NIST) assisted with the investigation and comparison of a standard activated flux composition versus the R type flux composition. A detailed, statistical analysis by Dr. William Russell of Raytheon Systems and NIST statisticians revealed that the use of a standard activated flux composition greatly reduced the amount of variation when conducting solderability tests. One of the major goals of the joint solderability working group is to develop test methods and standards promoting consistency.

Safety Concerns

The primary rationales for using an R type flux are: 1) colophony or rosin contains only naturally occurring flux activator constituents and is not subjected to the problems/complications of chemistry formulas by the flux supplier and 2) the industry acknowledges and accepts that, if a component or PWB surface is found to have acceptable solderability test results using R type flux, then more active flux formulations used in the assembly process are likely to produce acceptable solder wetting results. This solderability assessment safety margin was a self-imposed, industry consensus decision.

The joint solderability working group understood the historical relevance behind the decision to use R type flux and had an equally strong desire to maintain a solderability assessment safety cushion. However, the member committees fielded a number of industry opinions to reassess solderability flux composition--based on technology improvements in surface finishes, improvements in flux chemistry formulations from flux suppliers and the desire to avoid an excessive safety margin that would impact cost and schedule. The committees conducted a number of tests that demonstrated, through use of a specific standard level of activation on real world, industry supplied component and PWB samples, that the occurrence of a false acceptable solderability test result was extremely low. No reported cases existed that exhibited a "pass ROL1 test--fail ROLO test Fail during board assembly" sequence.

Global Standardization

A second major goal of the joint solderability working group is to develop test methods and standards that promote global standardization for the electronics industry. The standard activated flux composition, selected and tested by the committees, is referenced in the International Electrotechnical Commission (IEC) 60068-2-20 soldering specification utilized for solderability testing. Having compatibility of flux composition requirements between the IPC/EIA/JEDEC J-STD-002, IPC/ECI J-STD-003 and the IEC specifications is a win-win situation for electronics assemblers and component/PWB fabricators.

The joint solderability working group has compiled a number of data sets during the two-year testing/ investigation effort. Review the test documentation, data sets and analyses that lead the solderability committees to propose the change to the flux composition. Many flux chemistry suppliers have been queried on availability of the proposed standard activated flux composition for solderability testing and electronics manufacturing, and a positive response was received from most suppliers.

Assembly Standards Update

The following industry consensus standards and guidelines have been published in the last quarter:

* IPC-HDBK-610, Handbook and Guide to IPC-A-610 (Includes IPC-A-610B to C Comparison), helps users understand criteria and provides the background needed for selection of such criteria. An extensive comparison of B to C revisions is included.

* IPC-HDBK-830. Guidelines for Design, Selection and Application of Conformal Coatings, assists designers and users of conformal coatings to understand the characteristics of various coating types, as well as the factors that modify those properties when coatings are applied

* J-STD-002B, Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires

* J-STD-003A, Solderability Tests for Printed Boards

* J-STD-20B, Moisture/Reflow Sensitivity Classification for Non-Hermetic Solid State Surface Mount Devices

* J-STD-032. Performance Standard for Ball Grid Array Bumps and Columns

* J-STD-033A, Standard for Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices

* IPC-D-356, Bare Substrate Electrical Test Data Format

* IPC-TR-5B3. An In-Depth Look at Ionic Cleanliness Testing

* IPC-2252, Design Guide for RF/Microwave Circuit Boards

* IPC-4552, Electroless Nickel/Immersion Gold (ENIG) Plating for Electronic Interconnections

* IPC-9151, Printed Board Process Capability, Quality and Relative Reliability (PCQ[R.sup.1]) Benchmark Test Standard and Database

* IPC-9199, Statistical Process Control(SPC) Quality Rating

The following standards are being balloted for industry acceptance:

* J-STD-004A, Requirements for Soldering Fluxes

* IPC.HDBK-OOS, Soldering Paste Handbook to support J-STD-005 Requirements for Soldering Pastes

* IPC-0040. Optoelectronic Assembly and Packaging Technology

* IPC-CM-770E, Guidelines for Printed Board Component Mounting

This summary and associated report were developed By David Hillman, Rockwell Collins; Mark Kwoka, Intersil Corp.; and Jack McCullen, Intel Corp. Those leaders acknowledge and express appreciation for the support of Dr. Carol Handwerker, National Institute of Standards and Technology; Dr. William Russell, Raytheon Systems; George Wenger, Andrew Corp.; Guy Ramsey, American Competitiveness Institute; and all others involved in the study. For the complete report, contact the author.

Jack Crawford is director of assembly, standards and technology with IPC. Northbrook, IL; [phone]; e-mail: JackCraw [e-mail]