IPC Standards Committee Reports — Base Materials, Fabrication Processes, Boards, Embedded Devices

Reports from IPC standards meetings at IPC APEX EXPO 2013 have been summarized to keep you up to date on committees’ work in advancing new and revised industry guidelines. This is the second report in the series.

Base Materials

The 3-11 Laminate/Prepreg Materials Subcommittee is revising IPC-4101, Specification for Base Materials for Rigid and Multilayer Printed Boards to its D revision.  Latest modifications to the C revision include: 1) The fracture toughness test method has passed Gauge R&R, so it will be included as an optional test and parameter; 2) Inclusion of another polyimide material specification sheet; 3) Obsolescence of at least six current specification sheets for which there no demand; and,  4) Clean-up of some errors in the document that have been present since the original release of IPC-4101 in 1997.  The task group also discussed redefining the FR-4 proposal for the UL 746E standard.  Additionally, the subcommittee addressed laminate and prepreg cleanliness issues during a presentation by the European Space Agency.

The 3-11f UL/CSA Task Group addressed the implementation of an RTI increase for PTFE materials in UL 746E from the previous 105OC to 130OC that was approved by STP Ballot.  UL is pushing this change quickly through their system.  Questions on OEMs utilizing the UL certification mark – Is it being used by board fabricators and/or laminators for their materials? – The answer appears to be “no”.  The task group also discussed the UL terminology change, “thin core” to replace the term “embedded materials” and its impact on industry. This was not resolved at this meeting but they will eventually be at future UL STP meetings.

The 3-11g Corrosion of Metal Finishes Task Group discussed the results obtained with MFG (mixed flowing gas) testing at three test facilities.  So far, the results are inconsistent.  Gaining correlation with these high levels of gas contaminants (H2S at 1700 PPB which is exceedingly toxic/mortal) is going to be challenging and so the work continues.

The 3-12a Metallic Foil Task Group covered a number of items, including: 1) Ballot on Amendment 1 to IPC-4562A, Metal Foil for Printed Board Applications, 2) Presentation by Wayne Case, Schmitt Industries, who manufactured the surface roughness standards for calibrating the various non-contact surface roughness measuring equipment and who is willing to pursue NIST traceability for these standards and 3) Jeff Loyer, Intel, presented on the effects of surface roughness on electronic insertion losses.  The group will hold a teleconference mid-March for all members of the 3-12a Task Group on the surface roughness measurements using the “standardized” roughness samples from Schmitt.

The 3-12d Woven Glass Reinforcement Task Group advanced IPC-4412, Specification for Finished Fabric Woven from ‘‘E’’ Glass for Printed Boards to its Final Draft of revision B. The group resolved all comments. The document will be balloted by the end of March for a 30-day period.

Fabrication Processes

The 4-14 Plating Processes Subcommittee completed the release of IPC-4556 Specification for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) Plating for Printed Circuit Boards by distributing hard copies to the subcommittee members present.  The Subcommittee discussed the revision efforts for IPC-4552 which needs full revision from its 11-year-old original release.  A round robin test program has been established and some efforts started.  Two test methods are proposed that deal with a) phosphorus content in nickel and b) proper stripping of immersion gold so as to get at the underlying nickel without damage.  The group also discussed the need for a specification for electrolytic nickel/gold (proposed as IPC-4557).  Additionally, the group discussed a phenomenon called “black tar” where lead-free solder is used for wave soldering applications with ENIG printed board finish.

Flexible Circuits

The D-11 Flexible Circuits Design Subcommittee reviewed new content for a future D revision of IPC-2223, Sectional Design Standard for Flexible Printed Boards. This included best practices for the design of circuits with controlled impedance, estimation of minimum bend radius for flex and rigid-flex printed boards, guidance on fabrication requirements for minimum surface conductor thickness, and guidance on HDI/microvia design.

The D-12 Flexible Circuits Performance Subcommittee reviewed industry comments to the final draft of revision C of IPC-6013, Qualification and Performance Specification for Flexible Printed Boards. Following this comment review cycle, the document is expected to go out for ballot in April.

The D-13 Flexible Circuits Base Materials Subcommittee celebrated the release of IPC-4203A, Cover and Bonding Material for Flexible Printed Circuitry and hard copies were distributed to the subcommittee members at the meeting.  The group then addressed the release of all three IPC-420X series standards to their A revisions.  Suggestions were proposed that ranged from an update of the 1998 original release IPC-FC-234, PSA Assembly Guidelines for Single-Sided and Double-Sided Flexible Printed Circuits to monthly teleconference addressing the amendments to the three A revisions of the materials specifications.

The D-15 Flexible Circuits Test Methods Subcommittee was notified that TM on propagation tear strength had been finalized and placed into the IPC-TM-650 prior to their meeting.  The subcommittee addressed initiation tear strength TM 2.4.16B at the meeting.  Other than determining what the jaw separation should be, the test method is nearing its final draft stage and will be sent to the 7-11 Test Methods Subcommittee review for comments.  Finally, the subcommittee decided that the D-15 Subcommittee should next tackle the revision of TM 2.4.9, Peel Strength, Flexible Printed Wiring Materials.

Rigid Printed Boards

With the publication of IPC-2221B, Generic Standard on Printed Board Design, in November 2012, the D-31b IPC-2221/2222 Task Group considered goals for a future revision C to the popular design standard.  Topics included addressing plated board edges (vertical edges), laminated bus bars, and flatness (warpage) of boards due to different packaging types (BGA, QFN, QFP, etc.).  Regarding the latter, the group agreed to wait until the completion of the IPC-9641, High Temperature Printed Board Flatness Guideline, in order to determine if IPC-2221 should provide reference to that document with associated guidance for the designer. The group also suggested that the IPC-2220 series be updated relative to HDI/microvia design rules so that IPC-2226, Sectional Design Standard for HDI/Microvia Printed Boards, could be cancelled, much like what is being down within the IPC-6010 series and the IPC-6016 HDI specification.

The D-33a Rigid Printed Board Performance Specifications and 7-31a IPC-A-600 Task Groups continued efforts for a future revision D of IPC-6012, Qualification and Performance Specification for Rigid Printed Boards. The task groups viewed presentations from subgroups actively working via a series of web conferences on the following subjects: metal-based printed board acceptance criteria, and an addendum to IPC-6012C that addresses lot frequency testing and periodic conformance testing with the new 1-10c test coupon within Appendix A of IPC-2221B.

An update was made of the work accomplished to date within the IPC D-33e Resolution Target Task Group.  This group expressed interest in generating a small document addressing visual acuity that would supplant IPC-OI-645, Standard for Visual Optical Inspection Aids, for visual acuity.  An acuity level could be established for specific levels of magnification inspection within IPC-6012.  The D-33e task group will establish data sets based on the usage of the USAF 1951 resolution target with a test method developed within the group.  The data will help the D-33a task group determine how to incorporate visual acuity requirements into IPC-6012.

The D-35 Board Storage and Handling Subcommittee reviewed the results of an industry survey that will help steer the revision of IPC-1601, Printed Board Handling and Storage Guidelines. Respondents provided information on the types of packaging methodologies as well as what surface finishes they typically use for printed boards.  The survey results will aid in a two-part process for revision: 1) Provide a set of baseline packaging procedures that fabricators may elect to utilize, and 2) Develop guidance on post-assembly packaging for maintaining printed boards up to final delivery to the user.

Embedded Devices

The D-55 Embedded Devices Process Implementation Subcommittee discussed the status of IPC-7092, Design and Assembly Process Implementation for Embedded Components. This document describes the design and assembly challenges for implementing passive and active components in either formed or inserted methodology on a printed board. The new standard focuses on fabrication and assembly processes and identifies various board types. It is expected that a final draft will be circulated for industry review in mid-2013.

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