Issue link: https://iconnect007.uberflip.com/i/393082
34 The PCB Magazine • October 2014 ed up using our standard F&S tables for the Rog- ers, and the Rogers datasheet F&S table for the Taconic. • Activation: Typically with FR-4 materials you can just go straight to metallization (elec- troless or direct) and continue processing. With PTFE materials, since they are Teflon ® based, you must activate the surface to enable the cop- per plating to stick. This can be done by using either a plasma unit or a chemical-based meth- od. If ponying up over $150k for a plasma unit from either March or Plasma Etch isn't in the cards, the chemical treatment method might be the way to go. Two such suppliers are Acton Technologies, Inc. (FluoroEtch) and W.L. Gore (Tetra-Etch). I've heard of people shortcutting this pro- cess, which may work for lower level commer- cial customers. However, when it comes to au- tomotive the best bet is to follow best practices. Just think how many recalls were caused by the motivation to save just a few cents on a part. No need to subject your company to that risk as OEMs are coming back to suppliers harder than ever to recoup warranty and recall costs. Technology: Power Delivery Systems The growing number of hybrid and fully electric vehicles are fueling a need for more advanced power delivery systems. Also, the in- creasing number of electronic functions is driv- ing battery manufacturers to find new options, such as lithium ion. From a fabricator's perspective, this means heavy copper PCBs (three or more ounces) could see an increase in demand. While double- sided heavy copper PCBs are fairly easy to do, multilayer buildups can be tricky. We'll touch on a few of the key things to focus on during manufacturing. • Stackup Generation: One of the most frequent failure modes in heavy copper multi- layer boards is voids within the bondsheet di- electric. Voids can subsequently cause high re- sistant shorts, CAF, and broken vias. One way to address this is by using as much 106 resin rich prepreg to fill the etched areas. Any leftover room in the stackup height can be made up by using 2116 prepregs as internal pads to push the resin into every etched out feature. Typically, though, with heavy copper you are waging a battle between minimum copper requirements and maximum thickness requirements. One trick to address this is by pre-filling the etched inner layers with layer fill epoxy, thereby mini- mizing the need for multiple layers of prepreg. Unfortunately, neither of these is a cheap op- tion but well worth the price when it comes to reliability of the end product. • Multilayer Lamination: Most tech- nologies allow you to throw in multiple part numbers using the same press recipe. However, heavy copper projects warrant their own recipe. Since you have a higher than normal amount of copper within the stackup, you should be using a higher temperature setpoint since that copper will act as a heatsink. Further, you should play with the rate of rise and pressure cycles to in- sure proper prepreg flow and etched area fill. • Etching: Most heavy copper projects will have you in inner layer etch at least 3x as long as standard inner layers. It's critical that you ad- dress the strength of the dry film being used. Most standard dry film will manage up to three ounces, but things get sketchy beyond that. It's important that to run development panels to establish the true limits of your dry film; it makes no sense to save 50 cents on dry film just to end up scrapping out a $20 inner layer core. Technology: Infotainment/Communications One of the newer technologies that has been a huge burden on automakers across the spectrum is infotainment/internal communi- cations. These technologies employ the use of Bluetooth, cellular, and sometimes even WiFi. If you look at the J.D. Power initial quality sur- veys, you will find that many of the premium marquees take a spot in the "Worst Performing" section, mainly because of their new driver in- terface systems. One of the most recently cases was the failures documents on the Ford Sync system. While many of these issues were due to software glitches, there has been a keen focus on hardware quality as well. These systems often PCBS FOR AUTOMOBILES: WHAT TO WEAR TO THE PARTY? continues