Tuesday, December 6, 2016
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Really Managing PWB Supply
Microscopic examination helps reveal defects in workmanship.

The harsh upheaval of the US PWB market has changed the dynamics by which suppliers and users of PWBs interact. Fabricators have become brokers, blurring the lines between manufacturer and re-seller. Further, aggressive roll-up companies have consumed dozens of former fabricators, eliminating their manufacturing capability while maintaining the name and sales activity but outsourcing the actual fabrication. Often this shift of production location has not been shared with the customers in a timely manner if indeed it has been shared at all.

Consumers of PWBs often find that boards they have purchased for many years have quietly shifted from an internal fabrication by a long-time supplier to an unknown outsourcing supplier. This shift has left the companies who use PWBs with three fundamental questions: "Who has my Intellectual property?" and "Are my fabrication specifications adequate?" and, "If adequate, are they being followed?"

The closely-knit customer/supplier relationships so common a decade ago worked very well because both parties viewed the arrangement with a common goal — to satisfy the end customer. Neither could be successful unless both were successful. The very thing that made these partnerships so attractive has become a major hurdle for consumers of PWBs in dealing with the shift of supply location. The reason is a long-time supplier of any product acquires intimate knowledge of the product to the point that drawings and specifications become important only when a change is needed. Often, there is a slow shift of the product support to the supplier from the customer. The customer may even reduce or eliminate internal technical resources and come to rely entirely on the supplier.
Chemical tests help reveal a PCB's innermost secrets.


This trusting, symbiotic relationship may seem simplistic when viewed through the lens of today's very sterile specification-driven procurement environment.

However, this bond of "trusting commerce" is extremely important to the success of the Book-of Business roll-up companies when the PWB purchaser discovers that a shift in production has occurred. If they also discover that they do not have adequate documentation about their PWBs, they are assured that the fabrication data is secure and they can continue to receive the boards. The fact that the boards are re-tooled relying solely on the prior fabricator's files is seldom brought to light. The customers are assured they will receive the same product and it will be made to the specified criteria.

Often, it is discovered that the PWB consumer has few internal specifications relative to the manufacturing process of the board, having only end product specs such as size and finish. The fabrication criteria is usually a reference to a class of the IPC A600 Acceptability standard.

IPC A 600H PCB Acceptability
Users and fabricators have collaborated for decades to create these standards. The importance of their position can be exemplified by the loss of prefacing figures (such as IPC A 600) and these being shortened to simply "Class 2" or "Class 3".

Consequently, the prevailing wisdom is that a fabrication shift is not a risk as long as the sales outlet provides a Certificate of Conformance (C of C) referencing an IPC standard. It is only fair to question prevailing wisdom by asking, "What is the validity or enforceability of a paper certificate from a supplier in another country?"

Have we become so complacent about accepting a paper C of C that we no longer understand its limitations? A new twist on an old concept is challenging this "paper" premise.

The old concept is outsourcing supply management. The new twist is applying this to Printed Circuit Board procurement. A mid-tier contract manufacturer (CM) was struggling with suspected PWB problems. The CM did not have adequate internal verification capabilities to determine if their PWBs were actually fabricated to the desired specifications. They could perform a visual inspection and do dimensional checks, but they could not evaluate copper thickness, cleanliness, surface finish, laminates, stack-ups, impedance, etc.

Management recognized the weakness of their system and understood that it could either limit their growth or cause the growth to be unprofitable. This was very disconcerting because the company had grown by 25 percent in the past 12 months and was expecting this growth trend to continue for several years.

The problem required an immediate solution that capital dollars alone could not solve. The reason was that when they analyzed the prior twelve months of activity, they determined that they had purchased over 350 different PWBs from 25 different suppliers, and generated over 1000 receipts. The time element required to develop the internal PWB assurance capability for this very high mix was unacceptable.

Management decided to take a different approach and formed a partnership with a broker that had a product assurance laboratory to assume total supply chain management for PWBs. Under the agreement, the PWB Supply Chain Manager (PWBSCM) immediately diverted all incoming shipments of PWBs to their assurance facility.

At the program inception there were 110 different PWB part number on order from twenty-five (25) different suppliers. The suppliers were all notified to change their "Ship to" address to the PWBSCM. The incoming product was subjected to laboratory analysis including: cross section, cleanliness testing, visual inspection, and complete Bare Board Testing. The criteria for acceptance was the IPC A 600 Rev H Acceptability Standard.

The results were not good, but they supported the opinion of management that they were at risk due to their inability to fully evaluate the suppliers. Of the 110 part numbers, 79 were received in the first 4 weeks (Lot 1) of which 61 percent passed (48 passed, 31 failed). Lot 2 consisted of 33 boards, and 65 percent of them passed (20 passed and 11 failed).

While 25 fabricators were "in play" more than half had fewer than 4 part numbers, and 5 had only 1 part number. It was interesting to note that the five vendors with only one part number had no failures. These five were the only suppliers to have a 100 percent pass rate. It is reasonable to assume that these were customer-directed and therefore were held to a higher standard by a customer other than the CM.

The PWB Supply Chain Management program with the CM has now progressed to the point where all incoming PWBs are being ordered and received by the PWBSCM. The aggregate pass fail data will be more difficult to assess for some time as there is a consolidation of vendors underway to remove all those who had poor pass rates. While it is anticipated that the pass rates for even the poor vendors would improve, they will not be given second chances. The reason is that their performance was evaluated when they were not anticipating that the product could (or would) be evaluated prior to assembly. While perhaps a harsh assessment, they have already demonstrated their business ethics.

PWBSCM Program Advantages
Since the program began, the CM has not experienced a single PWB related failure. This is extremely important as the agreement with the CM includes a compensation for the value added to a defective PWB (normal warranties are limited to the value of the PWB). Additional metrics are being collected by the CM relative to first pass yields, process defects, and customer returns. Early and (unscientific) evidence shows significant improvements in all of these areas. Further, it is anticipated that total inventory dollars will be reduced by having a PWBSCM focused entirely on managing the flow of PWBs. Safety stocks become the problem of the PWBSCM which frees up working capital for items central to the CM's core competency.

Purchasing, receiving, and inventory resources can be re-allocated to other priorities as they no longer are required to handle the PWB process. Incoming inspection is eliminated as bar code labels and vacuum sealing in standard lots go directly to stock with only a label scan. Freight costs are reduced as shipments are consolidated. Last, Business Development can access knowledgeable and trustworthy resources to assist with quoting and directing customers into the most suitable technology. In essence, the CM has recaptured all the advantages of the captive PWB facilities of long ago with none of the costs.

Elements Required
A successful PWBSCM program requires a number of key ingredients. Offering only procurement assistance is not adequate. The supplier performance data collected at the program's inception indicates that there is significant risk if C of Cs and supplier quality credentials (ISO, etc.) are the only evaluation prior to assembling parts on the PWB. Therefore, a successful program must have as its objective not only that PWBs are available when needed, it must ensure that only good PWBs are being assembled. To achieve that goal the following elements are essential:

  • Total management commitment to the program by the CM or OEM.
  • Experienced PWB engineers at the PWBSCM.
  • Front end software for PWB fabrication capable of doing Design Rule analysis.
  • PWB CAM software for Arrays and file modifications.
  • PWB inspectors trained in the IPC acceptance standard.
  • Analytical laboratory capable of analyzing all major PWB characteristics (copper thickness, surface finish, interior construction, solder float, Ion Chromatography, X-ray fluorescence, isolation resistance, non-contact coordinate measurement (CMM).
  • Bare board testing (Flying Probe).
  • Board Modification capability (routing, marking).
  • Re-packaging equipment for vacuum sealing.
  • Extensive ERP system to manage inventory and customer MRP linkage.
  • Supplier Management Program by PWBSCM that includes, but does not rely solely on annual audits. The system must collect supplier laboratory performance data about each shipment in addition to normal procurement metrics.

A successful PWBSCM program is not about a gate keeper that sorts out the bad product. It is about developing a supply chain that delivers quality product consistently. The gate keeper then becomes a facilitator and enabler allowing the CM or OEM to better utilize their capital resources without fear of damaging their business.

Contact: DIVSYS International, LLC, 8110 Zionsville Road, Indianapolis, IN 46268 317-405-9427 fax: 317-663-0729 E-mail: sales@divsys.com Web:
http://www.divsys.com


 
 
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