Issue link: https://iconnect007.uberflip.com/i/1143487
50 PCB007 MAGAZINE I JULY 2019 4. Create Fabrication Data That References IPC Specifications Having requirements per IPC standards cre- ates a clear expectation for your supplier with- out getting too specific. Examples of specifica- tions to reference include: • Material per IPC-4101 • Acceptability per IPC-600 • Manufacturer to IPC-6012 Class X • Surface finish per IPC-4552, IPC-4553, IPC-4554, etc. Being too specific when telling your sup- plier what the design requires can potentially cause unintentional costs. For example, it may seem like a good idea to specify an exact ma- terial from a precise brand to ensure adequate control. It may seem contradictory at first, but unless the design absolutely requires one spe- cific material only, it might be safer to specify an IPC standard and benefit from a number of approved brands. With some latitude, the factory will then be free to choose the mate- rial with which they have the greatest experi- ence and is best suited to their manufacturing processes. Forcing a specific choice on the fac- tory can create problems since it could intro- duce additional yield risk upon the reliability of their processes compared to using a material the fabricator is familiar with. 5. Copper Weights NCAB recommends specifying copper per the IPC copper table in the IPC-6012 and IPC- 600 specifications. IPC does not specify copper in terms of ounces per square foot but instead specifies in terms of finished thickness in mils and microns. A common example we frequent- ly see is a request for 2-oz. copper on the out- er layers. Most manufacturers will accomplish this with 1-oz. base copper and Class 2 plating for a finished thickness (after processing) of 47.9 µm (1.886 in.). This can affect reliability if the PCB was designed with an expectation for 70-µm (2.80-in.) copper on the outer layers. Conclusion Overall, it is important that your PCB sup- plier quote with standards and reliability in mind, not solely on price. Providing the pre- viously mentioned documentation and details will help ensure yield reliability without incur- ring any unnecessary costs. IPC standards are a useful guideline with which to work but be sure to always evaluate the ultimate function of the board and adjust your design and build re - quirements accordingly for manufacturability. There are many factors to consider when first designing and then transferring a board to a supplier in order to build a reliable PCB. Be prepared to answer questions to make sure the PCB performs as required. It is important to choose a supplier who values quality, takes full responsibility for production, and works with you as a partner to help produce a reli- able PCB. PCB007 Jeff Beauchamp is a field applications engineer with NCAB Group.