PCB SOURCING
Smarter Software canimprove your alternate partS
Smart software can help procurement specialists add value and contribute to overall success on the factory floor By Bruce Isbell, Valor Division,Mentor Graphics
Mentor Graphics’ first article in the June 2010 edition of ESNA listed an overviewof sixways that current software technology used specifically in the electronics assemblymarket can help buyersmake even greater contributions to the overall success themanufacturing operation. These sixmethodswere:
1. Building an alternative components list 2. Validating themanufacturability of all components 3. Linking incoming inspections to themanufacturing database 4. Improving inventory accuracy and visibility 5. Reducing inventory through leanmaterial flowcontrol
6. Linking the supply chainwith actual quality data frominspection and test during assembly. In the second part of a series on smart software,Mentorwill dig
into the details of these improvedmethods to add value to the traditional role of the professional buyer.
Building up the perfect avl It’s clear that having an extensive list of alternate or interchangeable parts in the Approved Vendor List (AVL) createsmore flexibility, better buying options, and helps ensure that component availability does not adversely affect production schedules. Of course it is expensive to stop production due to a parts shortage, but it is even more expensive to stop productionwhen a part delivered to the line turns out to be awolf in sheep’s clothing. By first appearance the partmay look the same as the previous reel or tray and even have the same internal part number (IPN). But at closer examination you may find there is a critical problemthatwas not screened before the part was added to the AVL (Figure 1).
The problemcould be one ormore of the following issues
1. Package shape, height or body outline
2. Pin pitch, pin length, and pin contact area
Figure 1: Parts that seemequivalent on paper sometimes prove to be unusable at themost expensive and inopportune time: during the assembly process
48 | September 2010
3. Moisture sensitivity 4. RoHS compliance
5. Pin-map, pin functions, signal tolerances
All five of these factors
must be equivalentwithin an acceptable tolerance for your process, butmost of the problemareas occur in the first four attributeswhich are all physical properties. Smarter software is the key to enabling effective screening of these four factors, and in the case of moisture sensitive devices (MSD) and RoHS, smarter software is needed to track these attributeswithin your inventory data and to control themovement and usage of these parts on the shop floor to ensure compliance.
Figure 2: Smart software automatically compares the dimensional attributes of pin pitch, pin length, pin contact area, and body length-width-height of the AVL parts in the BOM
physical attributes for best avl screening Engineers who develop the schematics for new product designs by necessitymust take care to select components with the correct pin-outs and functional performance. They also look for component packages that fit their plan for the formfactor of their product. This is often a give and take process, until the engineer settles in to a parts list that he believesmeet his criteria for a successful electrical andmechanical design.
The professional buyer should now have early visibility to the
engineer’s component requirements, listed typically as the engineering bill ofmaterials (eBOM) for sourcing. This should be available to the buyer even before the PCB layout gets to the stage of component placement. Now there are tools available to assist both engineering and procurement in the build-up of a complete parts list, including alternate parts in the AVL that are truly interchangeable (Figure 2).
Using technology illustrated in Figure 2, the buyer can take the
eBOMfromengineering and quickly determine if there is geometric equivalencewith components chosen fromthe AVL. This is a true value added service that not only helps engineering in their component search, but is also extremely useful in cleaning up the entire AVL. Often physical package equivalencies are taken for granted only to be proved false downstreamwith the stakes are much higher. Geometric equivalence is crucial for true interchangeability overall, but for the given project it is equally important that the correct package intended by the engineering design is used. Here again technology is available to ensure there will be equivalent solder joint performance intended by the designer
www.electronics-sourcing.com
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