IPC7351-C Draft or Release date?

I worked on both committees and I’m familiar with all the differences, however, I joined the SM-782 Land Pattern committee in 1999 and there were no further. IPC had an on-line web-based SM-782 Calculator and Jeff Mellquist and I created a similar IPC-SM-782 calculator using Excel spreadsheets in 1999 & 2000 and shared it with IPC, Dieter Bergman and Gary Ferrari. Jeff and I used the same mathematical model to test our results against the online calculator and discovered some funny math that was going on in the SM-782 publication. For some reason that we don’t know, IPC left out important rounding calculations and left the readers to assume several key calculations. Jeff and I are mathematicians and we used the math that was printed in SM-782. We could not create a working calculator that accurately reproduced the on-line IPC calculator results because the entire IPC mathematical model for pad size and spacing was not printed in the standard. 

Note: 50% of the publication of in SM-782 were package and land pattern dimensions. This data was fabricated by the committee 10 years before I joined. I eventually discovered that none of that data was used by any component mfr. and the land pattern dimensions were created as a guideline and not a standard. i.e.: all of the dimensional data was a fictious fabrication (not real-world data). I proved that when I created the content for the new IPC Calculator, no manufacturer dimensions matched IPC-SM-782 package dimensions.

At the 2001 IPC APEX conference, Dieter and Gary handed me documents that they obtained from IEC in Europe that described a 3-Tier PCB library system. Jeff & I then created a 3-Teir calculator and abandoned the SM-782 calculator. Our comparison results between the new 3-Tier calculator and the old SM-782 calculator was that SM-782 land patterns were larger than Nominal but smaller than Most density levels.

IPC BOD created a Pin # for the creation of a new Standard called IPC-7351. Jeff and I flew back and forth to Chicago to meet with Dieter Bergman and John Perry to write the draft of 7351. Once a year Gary Ferrari attended our 3-day meeting. I created a Land Pattern Naming Convention that I contributed. I helped Dieter upgrade graphic images, tables and charts for 7351. Took the SM-782 and upgraded it to 7351, but the mathematical model stayed the same but with new Solder Joint goals for Toe, Heel and Side values. During this intensive upgrade, Dieter asked Jeff and me if we could create a software program that could be distributed with the new 7351 document and we agreed and signed an MOU with IPC. Then IPC removed the SM-782 on-line calculator from the internet.  

In 2004 PCB Libraries, Inc. was formed to distribute the new 7351 calculator, even though 7351 was not released yet. In 2005, IPC-7351 document was released, and the PCB Libraries LP Wizard Calculator came with the purchase of the new standard. The MOU between IPC and PCB Libraries lasted until October 2017 when out of the blue, IPC discontinued the MOU and that decision was based on a committee member from Mentor Graphics and Karen McConnell, the committee chair person, who claimed that the MOU broke the new IPC anti-trust law that states IPC will not promote any CAD vendor or PCB manufacturer. Even though PCB Libraries, Inc. supports every CAD tool in the electronics industry. The MOU agreement was canceled, and IPC no longer provides a free IPC Calculator with the sale of the 7351 standard publication. Gary Ferrari told IPC that their decision to end the MOU was a foolish mistake on their part.

During the creation of IPC-7351A Jeff Mellquist discovered a new bug in the IPC mathematical model that affected the “Heel” joint. Dieter Bergman’s excuse for this was that the Heel needed to be longer because it was an assumption that 70% of the solder joint strength was in the Heel. But this proved to be inaccurate because the longer Heel placed the pad under the package body. Then component manufacturers started to make the package stand-off very small, even 0.00 and the pad under the package didn’t make any sense. IPC upgraded the mathematical model to make the Heel shorter.

YTD 2018, the current committee has decided to remove the Fabrication and Assembly Tolerances in the upcoming release of 7351C. Leave them in the Calculator but turn the values to 0.00. This will have a minimal impact on the resulting land pattern as the pad sizes will be 0.01 – 0.04 mm smaller.

The bottom line is that IPC could never create a working calculator that produced repeatable reliable results until Jeff Mellquist and I created our calculator. Along the way, we discovered fuzzy math and inconsistency due to what we refer to as the Dieter fudge factor, where he twisted the math to create a result that he accepted. But we needed to create a calculator that provided consistent results without fudging the numbers.