IPC released Revision B to IPC-6012, Qualification and Performance Specification for Rigid Printed Boards, and Revision G to IPC-A-600, Acceptability of Printed Boards. Together they represent the core IPC documents for describing the acceptable and nonconforming conditions that are either externally or internally visible on finished printed boards and the frequency of end-product inspections.

Connected at the Hip

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From its inception, the revision path for both IPC-6012 and IPC-A-600 was intended to be a synchronous, fluid effort between the respective IPC D-33a and 7-31a task groups that are responsible for them. Starting with the initial planning meetings and progressing from each draft cycle all the way up to the final balloting process, the two groups met, reviewed, commented and voted simultaneously to achieve maximum compatibility between the two standards. The effort underscores the close relationship between the two documents: IPC-A-600 relies on IPC-6012 for the minimum acceptability requirements for printed boards and the acceptance testing frequencies required for printed board manufacture and procurement, and IPC-6012 relies on IPC-A-600 for visual support and interpretation of those requirements.

Enhancements to IPC-A-600

Revision G of IPC-A-600 incorporates over 80 new or revised graphics and photographs to better illustrate acceptance criteria within IPC-6012. Existing sections, such as those for measles, dewetting, conductor width, etchback and foil cracks, have been updated with new or enhanced images. The document has been updated to better define the concept of thermal zones for evaluation of laminate voids, and definitions for internal and external annular ring have also been revised. Where possible, illustrations have been replaced with photographs to better describe IPC-6012 requirements.

New sections have also been created to address lifted lands prior to thermal stress, smear removal resulting from plated-

through hole formation and surface plating requirements for wire bond pads.

Figure 1. Wire Bond Pad.

Figure 1 shows an example of wire bond pad coverage in IPC-A-600G.

IPC-A-600G flex and rigid-flex board performance criteria was updated to match the criteria established in IPC-6013A, Qualification and Performance Specification for Flexible Printed Boards. Previous versions of IPC-A-600 lacked strong coverage of IPC-6013 performance criteria. Illustrations and photographs have been incorporated or updated to address coverlayer coverage, adhesive squeeze-out for both lands and foil surfaces, access hole registration and laminate integrity for both flexible and rigid-flex printed boards.

Figure 2. Laminate Integrity for Rigid Flex.

Figure 2 shows updated coverage for rigid-flex laminate integrity.

Enhancements to IPC-6012

A significant number of changes can be found in Revision B to IPC-6012. Acknowledging advances in surface finishes and hole densities, table 3-2, which describes minimum plating thicknesses, has been updated to address nickel under gold for wire bond applications, electroless nickel/immersion gold (ENIG) and microvia structures. Coverage of defects within solderable lands has been expanded to address BGA pads and wire bond pads in addition to more detailed requirements for rectangular surface mount pads.

Figure 3. Defect Allowances within Round Surface Mount Lands.

Figure 3 provides an example of round BGA land coverage. Minimum conductor thickness tables for both internal and external traces have been expanded with separate criteria for Class 1, 2 and 3 end-product, and variable processing allowances have been incorporated, which account for scrubbing of copper material in the fabrication process. A new section has also been created that discusses hole size, hole pattern accuracy and pattern feature accuracy.

An important addition to the section on internal annular ring requirements provides guidance on the issue of whether or not misregistration can accurately be evaluated, based on how a microsection cut is “clocked” or rotated.

Figure 4. Comparison of Microsection Rotations.

As Figure 4 shows, a test coupon cross-section may or may not reveal misregistration depending on the rotational orientation of the sample.

Table 4-3, which establishes the acceptance testing frequency of samples based on end-product class and lot size, has been updated to reflect the A/B plated-through hole evaluation coupon for structural integrity after thermal stress testing. The A/B coupon is a novel design that was first introduced in Revision A to IPC-2221, Generic Standard on Printed Board Design, in 2003 and allows a single microsection coupon that can evaluate both large and small holes.

IPC-6012B also unveils a performance specification slash sheet for space and military avionics. Based on existing OEM industry specifications, this specification sheet provides exceptions to IPC-6012B Class 3 requirements for use by the aerospace and military avionics sector of the electronics interconnect industry. To date, IPC has received interest in similar performance specification sheets for the telecommunications and automotive industry segments and encourages other segments of the industry to contact IPC for future performance specification sheets.

Don Dupriest, Lockheed Martin Missiles and Fire Control, chair of the IPC D-30 Rigid Printed Board Committee, commented on the applicability of IPC-6012B to current printed board technology: “The release of IPC-6012B, together with IPC-A-600G, represents an aggressive attempt to stay current with performance requirements of present technology. As an example, the scope of IPC-6012B has been modified to form a better relationship of the sub-tier document IPC-6016 to assist in high density interconnect (HDI) fabrication documentation.

An optional identifier system has also been established to provide clarity of the design technology being employed. Technology codes have thus been created to quickly identify the specific technology employed in the design. This should help PCB manufacturers’ sales and planning departments to immediately recognize resource discriminators for build requirements. In particular, the final finish of the product is one area where designs are seeing increasing variability. Users are encouraged to make use of the updated codes in section 1.3.4.3 to clearly identify finish requirements.”

No Rest for the Weary

With the release of these two documents, the IPC D-33a and 7-31a task groups won’t have much time to rest. In October, the two groups will reconvene at IPCWorks® in Minneapolis, Minn., to go over a wish list of items for the next set of revisions. Already on tap for future discussion are magnification levels for visual inspection, board cleanliness requirements, board storage and handling requirements and criteria for embedded passives. “The task groups were sensitive to future requirements to support embedded passive devices,” noted Dupriest. ”The IPC-6012B now recognizes the use of these materials. Futures goals include incorporating performance elements as they become defined by the IPC D-37 Embedded Passive Devices Subcommittee working on embedded passive technology.”

Giving credit where credit is due, Dupriest added: “The IPC D-30 committee leadership would like to thank all of the individual contributors that helped fine-tune the IPC-6012 and IPC-A-600 into the current synchronized documents. Special thanks also go to all of the IPC-A-600 certified trainers who have provided valuable feedback from their instruction experience that will, in turn, facilitate a stronger certification program with this new release.”

To be notified when the IPC-A-600G and IPC-6012B are released, please visit www.ipc.org/NewReleaseSignUp.