Eight steps for efficient PCB manufacturing and assembly(part 1)

PCB manufacturing and assembly is a crucial stage that stands between thedesign of every technology device and the finished product. Critical businessmetrics - cost, quality, delivery, etc. - are directly affected by the quality of themanufacturing process. Today, PCB manufacturing performance andproductivity are under threat as customers’ delivery requirements become morevolatile and pressure on both the engineering and materials infrastructurescontinues to grow.In this dynamic environment, successful PCB manufacturing must follow eightsteps. This is the first in a two-part series and we will look at four of those stepsin each. Here is the initial quartet: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 processThe second set of steps, covered here in Part Two, is:1. Stay on top of materials2. Develop efficient exception management3. Ensure assurance, conformance, and compliance4. Deploy seamless operational managementFor now, however, I’ll explore each of those first four concepts in more detail.

1. Kn

The manufacturing product model is one of the most significant uncontrolledvariables. The late-stage cost of re-spinning a design or implementingcountermeasures due to production issues can be several orders of magnitudegreater than that if a problem is resolved earlier. Moreover, a delay to newproduct introduction (NPI) can result in major lost business opportunities if youfail to reach customers on time.You must accurately and thoroughly understand the PCB and its requirements.The manufacturing processes need to match the product’s requirements in a waythat is efficient and that ensures quality. Designs should be checked againstmanufacturing standards as they arrive for fabrication and before themanufacturing engineering processes begin.Industry-leading PCB design for manufacturing (DFM) tools mitigate risk andpromote product quality. The most advanced DFM tools are based on rulesderived from actual process capabilities and configurations. They analyzedesigns in seconds and then highlight opportunities for cost improvements inmanufacture, yield, quality, and testability. Hundreds of tests for PCB fabricationand assembly can be performed that provide clear recommendations to improve alayout improvements, yet without the layout design engineer needing anymanufacturing expertise.

Advanced DFM tools use data formats such as ODB++ to represent the completeand accurate manufacturing product model, without that model being weigheddown by supporting documentation. Manufacturing receives all the necessaryinformation needed to fabricate the PCB itself and assemble the final product asthe designer intends, without the need for data reconstruction.

Traditionally, the first step taken when a new product is introduced to PCBassembly manufacturing is to prepare the design and related data for a specifiedset of processes. From the production point of view however, rather than anassumed and therefore fixed manufacturing configuration, the manufacturerreally needs to prepare several production configurations from which to choosethat which best meets the requirements of the customer at a given time.Shopfloor planning needs to determine production times, rates, and quantities foreach product, based on this choice of capable production processes that meetdelivery requirements. As the number of concurrent discrete products increasesand tolerance for finished goods stock decreases — whether in the factorywarehouse or a shrinking supply chain — lot sizes have to become smaller andthis requires a much higher degree of production interleave than before.Enterprise resource planning (ERP), manufacturing execution systems, andgeneric shopfloor optimization software are not that good at finding efficientways to manage mixed production strategies. They force an unavoidable tradeoffbetween the flexibility of a higher mix of products against productivity. Planningsystems must quickly analyze a project’s shopfloor status, consider changingdelivery requirements, and understand PCB process optimization opportunities.That last step requires an ability to survey the project at a high level and simulatematerial setups, product groupings, within the context of machine and lineoptimization. The inherent complexity of surface mount technology (SMT)process makes it extremely difficult to achieve these goals.

The inherent complexity of surface-mount technology raises many challenges (Source: Peripitus)

The most common tool used for this process is Microsoft Excel, which canhardly be expected to be able to find the most optimum production plans forSMT. Fortunately, SMT-orientated Production Plan logic is now available thatsimultaneously optimizes the selection and sequencing of products according todelivery schedules, whilst simultaneously grouping products and feedersthroughout the SMT processes.This approach reduces SMT changeover time and optimizes machine utilizationand efficiency. It also creates a production schedule that accurately reflects theneeds of the customer, and minimizes stock dormancy in the warehouse andbeyond.The top-level plan is derived from standard ERP tools together with therequirements for each product, which are then broken down for each line andmachine. The Production Plan logic is capable of optimization based on real-timecustomer requirements, the current production status, and the inventory ofavailable materials. Such tools can manage thousands of products over a periodof time and perform optimization for the whole shopfloor, applying a flexible setof rules that determines planning policy and priorities.The result is an immediate increase in operational productivity, with high-mixPCB production achieving levels of efficiency approaching those for

high-volume. The ability to respond rapidly and precisely to demand changesmeans that the factory can be flexible without having to resort to accumulatingstock of each of the products or sacrificing performance.

SMT engineers generate production-ready machine programs, test and inspectiondata, and visual documentation by converting the manufacturing product modeldata and a local bill of materials (BOM). That BOM usually comes from the ERPsystem.This is the first step taken at electronic manufacturing service (EMS) companies,where an understanding of the cost of PCB production is required, along withany specific physical project requirements (e.g., safety-critical requirements forautomotive applications).Carrying out complex process preparation can be very difficult. It starts with theproduct data qualification and merger of the local BOM data. This step oftenencounters discrepancies that must be resolved before other processes can start. Itis important to get a full understanding any new materials that are being used(e.g., how they are supplied and what sizes and shapes are available, etc.).Then the SMT assembly work has to be split across different machines in anyspecified configuration. These machines may run on different software platformsor come from different equipment vendors. SMT-related processes (e.g., screenprinters, reflow ovens) also need to be set up.A similar process flow has to be created for each of the test and inspectionprocesses, whether these are manual, automated or a combination of both.Finally, comes the operator documentation.Performing all this for each PCB product often consumes the availableengineering resources, particularly in a time when the number of products andthe product mix is increasing. As a result, defacto assumptions are inevitable, andthese typically lead to restrictions that limit each product to a specific lineconfiguration. Therefore, there are effectively very few, if any choices, aboutwhich SMT line is assigned to any product.Frequently to make life easier, many manufacturing lines will have the sameconfiguration, eliminating any choices in the production rates that can beachieved. This leads to a situation where some lines frequently build to stock notrequired for delivery, while other lines stand idle. Delivery targets for someproducts become unachievable.This is changing thanks to advanced Process Preparation tools. They take thedesign data and merge the BOM within a graphical interface, allowingdiscrepancies to be quickly identified and resolved to create a single productdataset.These tools can generate optimized SMT program sets, test programs, inspectiondata and more. They can identify all the necessary PCB manufacturingengineering process steps across equipment from multiple vendors. Directoutputs to SMT machines, testers, and inspection machines can be sent without

manual data manipulation, using sophisticated automated native program andlibrary generation tools.All engineering processes share a common-parts-shape data source, linked withthe ODB++ product model data and the web-based shape library. Simulation ofthe SMT machine operation is performed in software to correct placementrotation and offset errors, removing the need for physical product qualification,and thus avoiding line downtime for NPI qualification.The SMT programming team can now respond to the needs of planning andprovide multiple line configurations for each product. That means that PCBproduction flows can now easily be matched to delivery timetables becausealternate configurations can be prepared in just a couple of minutesThe results include reduced NPI lead-time, increased asset utilization, theelimination of line down-time for product qualification, and a reduction in theengineering effort to duplicate data maintenance across different systems.Overall, there are general increases in machine optimization, line balance, testcoverage, reliability and yield, and assembly operation.

SMT machines are now very fast, and SMT materials have become very small. Itis impossible to follow the operation of SMT machines with the naked eye.Multiply the inherent challenge here by the number of machines across all thelines on the shopfloor. Now ask yourself how can even the most experiencedindustrial engineer be expected to diagnose and explain sudden drops inperformance or find the causes of unexpected quality issues using traditionalinspection techniques.This affects both the reliability of on-time delivery of products, and stresses theassociated production resources and materials supply chains because they cannotbe synchronized effectively to requirements. Planning changes required to meetchanging demands can be very risky to execute because of all the unknowns thatneed to be assessed. Materials will have been physically committed to productionin terms of kit preparation; work-orders may be partially completed withassociated part-built work-in-progress at several locations.The true utilization rate of equipment is also often unknown: State-of-the-artmachines incorporate multiple heads, multiple conveyors, and multiple modularstages, and this combination can hide significant avoidable idle time. Also, thetiming of changeovers between products cannot be predicted accurately whichcreates bottlenecks. These percolate right through to issues such as whichoperator performs which task. Reports created using data extracted fromindividual machines have little meaning because they do not consider the fullcontext of events, specifically the effects of external causes of stoppages.The situation is so dismal, that manual data collection or simple PCB counting isstill often the norm. Data from the SMT production process generally hasminimal value. It is inaccurate, incomplete, unqualified, and arrives too late to beacted upon. All this creates a huge limitation for successful productivity

improvement initiatives, planning optimization, material delivery, and resourcemanagement.Here again, the introduction of advanced capabilities is providing newapproaches that can collect and process data in real-time no matter what type orvendor of SMT machine or related process, including manual operations. Eventsand supporting data are read and normalized, eliminating differences in the dataformat and meaning, and harmonized for a single common language. Datacollected is automatically qualified.For example, when a machine stops, the production line can be analyzed to seewhy the flow of PCBs has stopped, or why the output conveyor is blocked. So,the occurrence and cost of any event during production can be accuratelyattributed. Information about complex SMT processes (e.g., under-utilization ofmodules or heads) is recorded and this exposes opportunities to improveproductivity. Event data collected even includes the precise usage and spoilage ofmaterials so that accurate material consumption can be reported.As the data is collected and processed live in real-time, it can be utilized by manyof the key operational and control functions. Use cases include the data’sexploitation by asset management to increase productivity, by materialmanagement for JIT delivery of materials to the line, and by production planningto implement changes that are exactly based on the current productioncommitment. This leads to an increase in productivity, improved reliability foron-time delivery, reduced on-site finished goods storage, and better planningchange execution that follows customer requirements.

This brings us to the end of our review of the first four necessary steps forcost-effective, high quality PCB manufacturing and assembly. Now read on tothe second part of this overview, where we take a detailed look at the next foursteps:1. Stay on top of materials2. Exercise exception management3. Enforce assurance, conformance, and compliance4. Employ seamless operational management

Michael Ford is Senior Marketing Development Manager in the Valor Divisionof Mentor Graphics.Having majored in Electronics, Michael started his career with Sony, gaining acombination of hardware, software, system architecture and manufacturing skills,leading to the creation and management of Sony’s global Lean Manufacturingsolutions in Japan.Since joining Mentor Graphics in 2008, Michael has become a key contributor tothought leadership in the industry, predicting trends and bringing insights onopportunities that can be gained by customers, driving the evolution ofmanufacturing execution technologies to deliver direct business benefits.