Printed Circuit Design & Fab - November 2008 - (Page 23)

DFM BaSicS 10. Board Thickness Another parameter worth considering, because of its implications on the card’s production, is thickness. The most appropriate card thickness for production is 1.6 mm, and it is advisable to plan according to this size. When card thickness is 1 mm or less, special handling is required. The thinner the card, the less rigid it is, causing its stability during production to fall. Mechanical support needs to be taken into consideration during the planning of cards. When there are components on only one side, a support plate can be added underneath the card to keep it stable. When components are on both sides of the card, a special device should be designed to support the card during its motion on the production lines. This device significantly increases production cost (in mass production, the additional cost will be less significant) and extends delivery time; therefore, it is better to place components on one side only. In conclusion, the linkage between planning and production of the printed circuit board is fundamental. Proper planning shortens time to market, reduces production cost and helps in achieving maximum production yield. When planning a circuit card, engineers must take into account the card’s production and assembly aspects in order to guarantee that fabrication is done right–the first time. pCd&f arBEl niSSan is COO of Circutec; ArbelN@nistecgroup. com. FiGurE 7. X-Ray – Design for Inspection. Minimize component overlaps, strong overlaps of the component populations on back and front side should be avoided, if possible. 8. PCB Marking Figure 7. Properly marking the electronic circuit contributes to quick and efficient production of the circuit card. This is beneficial both for automatic machines, like AOI, and for manual work performed on the card, like quality control, electric testing, rework and repair. It is necessary to ensure that the components are organized on the face of the circuit in a logical and consistent order and according to their allow the engineer to proactively improve the design, saving time and money. This step will make it easy to locate them during production. Markings should be full and complete and not hidden by pads and mechanical holes. Make sure that markings remain visible after applying the component to the card. In addition, for components with multiple pins, we have to mark pin number “1” near the relevant pad. It is also advisable to add near every tenth pin its number, this enables fast location of the component’s pins. Components having polarity should be marked with “+” to indicate the direction of applying the component, as well as the direction of electric current in diodes’ components. 9. Planning Fiducial Points The fiducial points on a PCB are meant to aid the automatic machines in the production line. Correct positioning of the points is cardinal for the success of card production, since the machines perform their accurate tasks based on these points; e.g. applying components, applying tin and visual inspection (AOI). Therefore, it is important to be meticulous when planning the card’s reference points. First, enable solder mask clearance, to prevent the points from being hidden and possibly reducing the application accuracy. Place at least three reference points on the card face in an asymmetrical form that can enable automatic machine recognition. This can confirm that the circuit was inserted into the machine in the correct direction. Avoid placing reference points in the margins, place them a minimum 0.25 inch from edges of the card. Be sure to place the fiducial on individual cards and not only on the panel. When using an automatic solder paste printer, place reference points on the solder mask and solder paste files. NOVEMBER 2008 printEd CirCuit dESign & fAB 23 http://www.pcb-pool.com http://www.pcb-pool.com

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - November 2008

Printed Circuit Design & Fab - November 2008 Contents Our Line Market Watch Around the World Happenings ROI Positive Plating Ten Tips to Improve Manufacturability 3D Chip-Package-Board Modeling Improving Circuit Simulation With The Addition Of Real Measurements Ad Index PCB West: Interview with NBS Design Inc. The Influence of Final Finish on Lead-Free Assembly Reliability The Lead-free Soldering Challenges for Peelable Resists Off the Shelf Marketplace BGA Bulletin

Printed Circuit Design & Fab - November 2008

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