Eight steps for efficient PCB manufacturing and assembly – Part Two

By Michael Ford

Second in a two-part series, describing critical rules that should underpin PCB manufacturing, andhow new technologies overcome increasing complexity.

In the first part of this series, we looked at the first four of the eight crucial steps that will help youachieve truly effective printed circuit board (PCB) manufacturing and assembly. Just to recap,those were:1.Know your product2.Do only what needs to be done - and only when it needs to be done3.Be ready to make anything in any quantity at anytime4.Know exactly what you are doing at each stage in the process

Now let’s take a look at the remaining steps towards achieving success in PCB manufacturing andassembly. These are:5. Stay on top of materials6.Develop efficient exception management7.Ensure assurance, conformance, and compliance8.Deploy seamless operational management

As before, I'll discuss each in turn, looking at technologies we can use to make them happen.

5. Stay on top of materials

The price of holding excess stocks of raw materials in the factory can rival labor cost differentialsin manufacturing in different locations across the world. Issues with PCB materials shortages haveprogressively shifted from the shopfloor to the warehouse. That does not mean they have beenresolved, simply that they have been moved somewhere else.

Relatively frequent stock checks have become essential across the entire factory becausesignificant discrepancies can accumulate between volumes recorded in the ERP system and thephysical volume of raw materials held on site. As a result, the minimum stock thresholds set forthe warehouse by manufacturing resource planning (MRP) systems are typically higher thannecessary. The MRP managers want to ensure there are enough materials to cover any re-orderlead times in the additional context of materials that may be 'lost' between physical stock checks.

Problems related to material logistics have also spun out of control as raw material volumes havebecome unmanageable on the shopfloor. There are often partially-used and improperly accountedmaterial reels left around at the end of work-orders. Specific PCB management requirements formaterials used in surface mount technology (SMT) processes (e.g., progressive moisturecontamination) are often compromised, leading to quality shortfalls.

As a result, customers' requests for changes to delivery schedules are sometimes deemedimpossible to meet because of the high risks associated with the unknowns around physicalmaterial availabilities. Then, there is the heavy workload involved in removing and/or reallocatingkits of materials.

To regain some control, new tools uniquely identify all materials in the PCB assembly factoryusing barcodes. These are attached to each material carrier, be it a reel or something else. Eachmaterial has assigned attributes that inform advanced stock management and tracking procedures,including support for SMT-specific issues such as the baking and dry storage of materials that areparticularly sensitive to moisture. These software solutions enable lean materials management,including Kanban control across multiple warehouses and managed locations on the shop-floor, aswell as the proper use and scheduling of just-in-time (JIT) deliveries.

Material selection from the warehouse is optimized for FIFO and many other configurable rules toreduce obsolescence, reduce search, improve location management efficiency, eliminate stock pickmistakes, and offer specialist oversight such as LED bin control. The correct stocks are verified inposition on machines at setup to prevent those machines executing with a wrongly locatedmaterial. Accurate live materials consumption information is synchronized with ERP tools toadjust re-order quantities and ensure the integrity of the inventory.

This eliminates the need for periodic physical stock checks, minimizes machine setup errors, andreduces re-work and quality failures. It also cuts the volume of material stocked both on theshopfloor and in the warehouse while increasing productivity and making it easier to reworkproduction schedules.

6. Develop efficient exception management

Successful PCB manufacturing can be thought of as the creation, one after another, of perfectproducts. Variation that affects the quality of those finished products threatens that overarchinggoal.

The PCB test-and-analysis regime has been developed to address defects that occur as a result ofproduction processes gradually or suddenly going out of control. Let's say, for example, that thereis a change in the material supplier. Although the new company may be qualified to supply under acommon internal part number, the switch can cause a sudden increase in placement errors if thereis just a small difference in, perhaps, height. Machines' visual detection algorithms can oftendetect these problems, which is good in terms of reducing placement errors but also results in an‘invisible’ spoilage of materials at the machine.

Many other problems and defects can slip through manufacturing, only to be discovered at test oreven later in the market. Along with material-related issues, process issues around screen printing,SMT mounting accuracy, and reflow can all lead to some degree of variation. The ideal scenariohas the test process act as a filter, ensuring that no defective products make it out of the factory.

However, the nature of PCB test means that this can never be guaranteed. Statistically, the greaterthe defect rate found inside the production operation, the greater the corresponding defect rate inthe market.

A key factor in reducing defects through test and repair is the speed with which defects aredetected and how quickly their prevalence across the factory is determined. Any delay between thedefect occurring and being detected increases the likely number of defective units. Several factorsdetermine the time involved. They include:Getting the unit into testCreating a repair ticketRouting the defective unit to a repair stationSearching for the defect and understanding the causeRecognizing the defectQualifying and recording the defectTaking corrective actionReporting the defect.

Because the consequences can be severe when a major defect is found, typically a PCB line isimmediately stopped, pending investigation.

To significantly shorten this process, advanced software can now capture test results and repairtickets electronically, assigning the results to each uniquely identified production unit. Such toolswill immediately flag a problem and this ensures the correct routing of a defective unit to therepair station. At the same time, statistical analysis is performed to determine whether a morewidespread problem has arisen.

At the repair station, the electronic repair ticket is automatically displayed with the manufacturingand test history and the product design layout data to speed up diagnosis. The softwareincorporates a statistically-based expert system engine. It can quickly analyze the symptom of thedefect on the repair ticket and then diagnose its root causes with reference to previous repairs.

This greatly reduces the time needed to find and process defects, limiting the scope of any qualityfailure. It also enables the statistical identification of out of control conditions while reducingdependence on specialist skills for defect and root cause analysis. The increased timeliness andaccuracy of quality reporting allows the manufacturer to change assembly operations swiftly,thereby reducing the extent of any defects. Fewer defects in the factory means fewer escape intothe market.

7. Ensure assurance, conformance, and compliance

There are high costs associated with finding quality issues once a product leaves the factory,especially those that have a safety- or business-critical element. This has led to two keyrequirements being placed upon PCB manufacturing operations for some time by that last group ofcustomers. Recently these requirements have also been imposed by an increasing number of

producers of high volume consumer products.

The first requirement is traceability. Should a defect be found in the market, the supply chain mustbe able to quickly analyze its source to determine what other units of the same product might havethe same problem. In automotive, successful traceability can make the difference betweenrecalling thousands of cars and a more controlled scenario where only a few hundred cars arerecalled.

The second requirement is conformance to designated operational standards. This is an attempt toreduce defects by making every operation follow a defined procedure. Conformance strategieswill likely have built-in checks that ensure that everything is performed correctly, in the rightsequence, and with the right setup.

Unfortunately, both requirements usually increase PCB manufacturing costs because they requireadditional human input, both to enforce compliance and to record processes. They can reduceproductivity as they add additional tasks and force temporary pauses in a line for manual datacollection. A lack of confidence in any manufacturing process can lead to the imposition ofcrippling procedures.

To promote compliance without impeding the PCB manufacturing flow, new software-drivenapproaches continuously gather data about materials and processes during operation. The dataincludes test results, the movement of units through production, materials placement and more.Almost all this information is collected automatically and associated directly with each specificproduction unit. The tools then generate complete traceability build records.

The software follows best practices. It enforces and checks correct operation as part of thestandard process. For example, it will verify the presence and composition of materials at the timeof machine setup.

Traceability is achieved at minimal additional product cost or effort because it becomes a built-inpart of the whole PCB manufacturing flow, not just the SMT machines. Automated analysis andreporting functions can build records on demand, so that any issue can be quantified and containedat a moment’s notice.

Conformance and traceability reduce the number of needless product recalls, enforce quality andcontrol costs. Moreover, the cost of ownership and operation for these tools are minor compared toprocesses that require manual data collection. In fact, when they are used effectively, these toolsoften deliver instead significant operational benefits.

8. Seamless operational management

Because of the complexity of SMT-based PCB manufacturing, different teams must assumedifferent roles across the flow, each with different motivations and incentives. The performance ofeach team is measured in different ways. This can lead to boundaries (or, commonly, 'silos') being

erected between various competencies, and a situation where operators, engineers and managersmay work well within their own specialities but do so far less efficiently at the boundaries of theirresponsibilities.

For SMT, specific competences that can become silos include production operation, productionmanagement, planning, supply-chain, quality, and industrial engineering. When an issues arises,each team may well have a different perspective, often leading it into conflict with colleagueselsewhere.

The complexity of SMT equipment requires the development of many different competences(Source: Megger)The complexity of SMT-led PCB manufacturing requires teams with varying competences (Source:Megger)

As a result, some problems can go unaddressed because a solution is perceived to entail more costthan simply 'letting it go'. Initiatives within or from one team may have detrimental effects onothers, and come to be seen as little more than 'flavor of the month' improvements. They can alsoquickly lose their attraction once attention becomes focused elsewhere. This limits realimprovement and results in far too many missed opportunities.

In a manufacturing environment built around a common PCB manufacturing softwareinfrastructure, everyone has a consistent view. Diverse information from different parts of theoperation is qualified, accurate, and timely. Everyone gets the same information from the samesource, but tailored according to each particular group's competences. This enables differentteams to work more effectively together, avoiding differences of opinion. Everyone can worktoward a successful conclusion.

Benefits include higher productivity and better quality. Responsiveness is more timely, fixes stayfixed, and a much more harmonious shop-floor working environment is created. For example, asdelivery timetables change, planning changes can be made and executed by each team within acontext that makes them part of their normal workflow.

Conclusion

The challenges that PCB manufacturing faces are not new. However, the complexity of today'sproducts and manufacturing processes mean that they can be much greater in both their scale andimpact. That highlights a now compelling need for change.

Volatility in customer demand is an inevitable by-product of consumers’ increasing influence onthe high technology economy, and also our need for more energy-efficient devices. In addition totheir complexity, today’s 'core' products actually tend to have many more variants and shorterlife-cycles. All this requires that factories adopt a step-change improvement in the flexibility oftheir operations.

Most volatility is due to a distribution chain where the elimination of buffer stocks has propagatedlurches in demand right through from consumers and commercial customers to the factory floor. Acomplete manufacturing operation needs to be re-engineered to enable it to efficiently reactwhenever timetables and product mixes change as a consequence of end-market turbulence.

In response, automation within SMT manufacturing is now extending from the machine andmechanical level into software. The complexity inherent in SMT technology is too great tomanage manually. It must be automated with regard to key data. Today’ s advanced softwarecapabilities provide a unique combination of support for the key areas, providing automatedcontrol mechanisms as well as a higher order of information for management purposes.

About the author

Michael Ford is Senior Marketing Development Manager in the Valor Division of MentorGraphics.

Having majored in Electronics, Michael started his career with Sony, gaining a combination ofhardware, software, system architecture and manufacturing skills, leading to the creation andmanagement of Sony’s global Lean Manufacturing solutions in Japan.

Since joining Mentor Graphics in 2008, Michael has become a key contributor to thoughtleadership in the industry, predicting trends and bringing insights on opportunities that can begained by customers, driving the evolution of manufacturing execution technologies to deliverdirect business benefits.