SMT007 Magazine

SMT-May2016

Issue link: http://iconnect007.uberflip.com/i/674146

Contents of this Issue

Navigation

Page 71 of 87

72 SMT Magazine • May 2016 machined glass epoxy carrier that is bonded to the circuitry. This can be the same material as is used to selectively apply discrete component stiffeners, thereby integrating the carrier pan- el and the component stiffeners into a single drilled and routed stiffener. Breakaway features separate the carrier from the circuitry after com- ponent assembly. Both these methods mimic the handling conventions of rigid printed circuits. Multiple-up panels inevitably result in a dis- cussion about defective parts within the panel matrix. False economy results when the con- tract manufacturer (CM) specifies a "no X-out" requirement. The CM wants to operate their equipment as efficiently as possible, and intu- itively this works best if they never deal with defective parts within the assembly panel. But this will often make the CM non-competitive on their bid to capture the business because of the premium paid for circuits. The incredible yield impact on the fabrica- tion house is best illustrated with an example. Suppose an assembly panel with eight circuits is required. If any of the circuits within the pan- el are defective, the entire panel is scrap. Even if the fabrication process is running at a 98% yield, the probability of all eight parts being good on a panel tumbles to 85%! As circuit den- sity, tolerances, and layer counts increase, yields of 90–95% are not uncommon. Using the same 8-up panel and a 92% yield, the probability of a defect-free panel is a mere 51%. These statistical calculations assume defects occur randomly on a panel, which is probably a stretch, but the illustration remains valid. Someone has to pay for all those good parts that are thrown in the trash can. The fabrica- tion house, seeing a 'no X-out' requirement, will quote the part assuming a poor yield. The likely consequence is the CM uses an inflated circuit cost in their BOM and doesn't get the contract, especially if they are competing with assembly houses allowing defects within the panel. Today's modern SMT equipment has the ability to recognize black marked circuits and will avoid placing components on these indi- vidual circuits. Most CMs recognize this ineffi- ciency is a legitimate cost expectation and are willing to concede some level of defective parts within a panel. The example with defective parts in a panel is a good illustration of the need for compat- ibility and cooperation among the members in the supply chain. Sub-optimizing at circuit fab may make component assembly much more cost-effective. Or vice versa. Lowest cost is of- ten achieved as a result of compromise. Under- standing the big picture will win the game. SMT Dave Becker is the V.P. of sales and marketing at All Flex Flexible Circuits and Heaters. To contact Becker, or read past columns, click here. A research into improving control of industrial robotic arms by doctoral candidate Maarten Essers of the University of Twente shows that the new generation of intelligently controlled robots is in fact capable of a quick and flexible performance of produc- tion tasks. In this new system, robots are not con- trolled in a top-down manner; instead they discuss what they are going to do next—allowing them to eventually assign and execute tasks individually (heterarchical approach). The new design architecture results in more flexible robots that are easier to use in smaller production environments. Essers' research is part of the SInBot project in which ten Dutch and German companies and research institutes are all working on a new robot platform. Breakthrough with New Generation Robots FlExiblE ciRcuit coMPonEnt aSSEMblY…and a MatH lESSon

Articles in this issue

Links on this page

Archives of this issue

view archives of SMT007 Magazine - SMT-May2016