Issue link: https://iconnect007.uberflip.com/i/1361971
96 PCB007 MAGAZINE I APRIL 2021 So, let's go to the source. We look into IPC- 6012E, the performance specification for rigid PCBs and supported by the acceptability stan- dard IPC-A-600K. Reading the first pages of IPC-6012E, the document scope, we find the first reference: 1.3.1.1: Requirement Deviations: Require- ments deviation om "these heritage classifica- tions" SHALL be as agreed between user and supplier. is means, anything you want that is differ- ent from IPC Class 1, 2, or 3 shall be specified. en in 1.3.3.1 we read: "e procurement documentation SHALL specify those requirements that are a result of the selection process within this specification. is in- cludes ALL references to AABUS. If the require- ment selection is not made in the procurement documentation including all related documents, then the default requirements in IPC-6012E Ta- ble 1-2 SHALL apply. en the standard gives us a selection sys- tem, and the default requirements. But frank- ly speaking, a lot of the requirements are not what you expect or are at least still open for discussion. As an example, the IPC-6012E still specifies solder coating as Sn63/Pb37. A Burden for the Buyer's Knowledge If we now jump to A-600K, the acceptability of the boards you receive, the "approach of this document" says, "is document cannot cover all of the reliability concerns encountered in the Printed Board Industry, therefore attributes not addressed in this issue SHALL be AABUS." So, using IPC standards for PCBs leaves a substan- tial burden on the buyer to know the standard and to specify requirements not clearly written in the standard. Quite a few attributes need to be discussed, unless you simply trust that your chosen sup- plier will be kind and accept a remake if the boards cannot be used as a result of wrong hole tolerances, or surface finish solderabili- ty—just because you did not mention the us- age of those boards. Back to the Workmanship requirement. We find this both in IPC-6012E and A-600K. Where IPC-6012 says, "Printed boards shall be ee of non-conformances in excess of those al- lowed in this specification," A-600K takes it to the next level stating, "Acceptance of imperfec- tions not specifically covered by this document SHALL be AABUS." For the discussion of those imperfections typically referred to by the PCB supplier as "cosmetic issues," please read my last column, "Attacking the Loophole at Does Not Exist." In IPC-6012E you find the term AABUS around 50 times (some are repeated in tables, etc.). In IPC-A-600K, it is mentioned 22 times. What does this tell us? It tells us that we have to be aware. Some of the attributes are not that important for all of us, but you can be sure that you will find some attributes impacting almost every printed board design. So, What Are the AABUS? The General One We already mentioned the selection process within IPC-6012E, paragraph 1.3.3.1, that in- cludes all references to AABUS and any re- quirement deviation—anything you need that is not mentioned in the standard. Or, if you want to combine IPC classes such as general requirements to Class 2, but copper plating to Class 3. The Most Important Ones 3.3.1: "When edge spacing is not designed in accordance with IPC-2222, nicks, crazing , de- lamination and haloing SHALL be AABUS." If you overlook this rule, you could easily be forced to pay for boards that basically don't meet your reliability requirements. Many de- signers are forced to utilise the space to the limit, placing traces closer to the outline that brings the design and the final PCB into this