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PCB Assembly

The Optimum Method is a set of proven processes that reduce cost, improve quality, and ensure on-time delivery.

Yes, we're different.

People often suggest we write up the methods we use for design and assembly. Typical things like layout rules, design for manufacturability guides, oven profile methods, inspection tips and tricks, and so on.

The problem is little tips and tricks won't solve your problems, reduce your cost, or improve your quality. What you really need is a process, a repeatable series of steps taken hand in hand with your contract manufacturer.

The Optimum Method is significantly different from what other EMS companies are doing. We discuss it in our Powerpoint presentations, and now for the first time we're publishing an overview on our website. It isn't theory, and it's not sexy or showy. Mostly it's just hard work. It does require experience, expertise, and intelligence. But history has shown it's successful at reducing cost and improving quality time and time again. So we just do it, everyday.

Here it is for EMS.

Quick Facts



Good Fit

Sophisticated, process oriented OEM's. Especially suited for customers seeking to reshore manufacturing back to the U.S.




Pleasanton, CA

Bad Fit

NPI only, consignment only, repair only, consumer (high volume/low value)

Cage Code



Mid-Volume Production

Price Leadership

Dazzling Performance



ITAR Registered

IPC 610 Class 3





Circuit Design

PCB Design & Layout

SMT Assembly

Through Hole Assembly

RoHS & Lead


Flying Probe

System Integration

Final Test

SBA Class

Small Business

Step 1: Early process preparation. Early - as in before we do anything else.

Applying lean principles to the early stages of a project is one of the factors most responsible for our phenomenal quality performance. When you request a quote from EMS companies their objective is to figure out a price (we know, we've worked at all the big EMS companies). At Optimum, we don't just 'quote', we begin the process of preparing to build. More fully detailed below, by the time you receive a quote from us we have cross-checked hundreds of elements of each component.

You need to perform a BOM scrub.

A BOM scrub verifies that your manufacturer/manufacturer part number combinations are valid. This should always be your very first step. Enormous amounts of time are wasted when this isn't done, and without it your ability to take advantage of downstream automation tools is greatly restricted. We prefer SiliconExpert for this. We have partnered with them for years, and through a special arrangement we contract directly with SiliconExpert's component engineering team to conduct most of our BOM scrubs, which they do for us overnight.

You need to know about ECN's & PCN's.

We don't wait to hear back from suppliers that one of your parts is obsolete. We collect the life cycle status of each individual component, but here's what a summary chart of your lifecycle data would look like:

Lifecycle Summary Report

You need to know if you're single sourced.

The percentage of your BOM that has multiple sources is a good barometer of overall risk. We provide you with line by line detail, but here's what a summary chart of your multi-source position would look like:

Multi-source Summary Report

Sometimes you need alternates.

When you do, wouldn't it be nice to have comprehensive report of alternates, including any differences and the predicted life of the alternate? And how about a link to the datasheeet? Viola!

Cross Reference Detail Report

(source: SilconExpert)

You need to know if your supplier has on hand inventory.

This is often one of the most vexing problems for small lot builds. Your supplier presents you with costs related to min/mults, but you think they should have the parts on hand from prior builds. Our systems automatcially checks each AVL'd manufacturer part number for 3 types of on hand inventory: on hand under your internal part number, on hand consigned inventory for you, and on hand unallocated inventory under another customers internal part number. These checks are performed automatically by our custom designed cost analysis software.

Descriptions are unreliable, your package types need to be confirmed.

Package types are critical to understanding labor costs and workmanship standards, and capability requirements. We pull the package types automatically from two databases (SiliconExpert and Mentor Graphics VPL) which each reference over 3 million parts. Our software recognizes 300+ package types and further categorizes them into 12 types for labor analysis..

Step 2: Design Review

Design for Manufacturing (DFM) is a broad term with a range of meanings. We refer to design reviews as Design for Fabrication (DFF), and Design for Assembly (DFA). DFF is a tool set used to review the design of the PCB prior to fabrication. Here we'll review DFA, which looks for problems that may cause rejects or other quality issues during assembly. Often associated with NPI, we run DFA on all products new to our manufacturing floor, and after any significant ECO's.

We use Valor.

Mentor Graphics Valor software is a suite of products for manufacturing. One of the modules runs a series of checks against a set of rules called Engineering Rule Files (ERF), that are specifically configured for the target manufacturing floor. Hundreds of tests are performed on every component and on every individual solder joint. Valor divides the tests into 6 categories and reports concerns (in yellow) and violations (in red) as summarized here:

Tens of thousands of solder joint checks

A typical 100 line item BOM might have 500 individual solder joint connections. We check each board for 242 solder joint rules, that's 126,000 tests (500 X 242). Here's some examples of what we check for you:

Solder mask coverage

Acute Angels


Silkscreen on pads

Component spacing

Via in pad

You receive a detail report by line item.

The Valor software reports a staggering amount of detail and can frankly be overwhelming. We have designed a custom report organizing the Valor output by prioritizing the issues. This is the report we provide to you.

We handle the interpreting

In truth you probably won't actually want the report above. Instead, you'll likely rely on us to review the report and let you know if there's anything you need to address (this is especially true if we designed the board). This is because we have in house design engineers, manufacturing engineers, test engineers, and world class PCB designers, so we have immediate access to the expertise necessary to interpret and act on the Valor DFA outputs.

Step 3: Open Book cost analysis (not quoting).

You need a partner, not an adversary. The partnership starts with working together to drive cost. We are big believers in the 'should cost' approach, which means you should understand the actual manufacturing costs of the products your outsourcing, not just the top line price. Most OEM's lack the resources or training to conduct this type of analysis. Instead of just quoting you a top line price, we provide you with a full cost analysis so we can work together to drive out cost.

Your costed BOM is the repository of your collected wisdom.

OEM's are often a little surprised when we point this out, but consider it for a moment. Which manufacturer has the best price for each component? Which vendor (as in distributor) offers you the best pricing and terms? Which package/temp range/RoHS/bulk or reel or tray or cut tape combinations is best for your circumstance? Have you leveraged your larger relationship to negotiate preferred pricing? The older the product, the more this type of knowledge accumulates in your BOM/AVL. This is especially true for custom items like cable assemblies, plastics, sheet metal, and machined parts.

So share it.

Apple, Cisco, and other leading outsourcers provide their costed BOMs. Why? Because it's dramatically more efficient and much more likely to lower costs. It's more efficient because we do not have to chase after low cost, highly custom, or poorly specified material. The odds of suppliers magically discovering lower material costs are actually quite low, especially for electronic components (see our article on how components are priced). We're much more likely to actually identify lower costs for you when we can focus our efforts on the cost drivers instead of chasing after every low value component.

What to collaborate, and what to compete.

In most outsourced electronic assemblies materials account for about 80% of product cost and we are not the direct source. The other 20% is labor, overheard, and profit which we are the direct source. We are both equally interested in the lowest material cost, so we are doing our best work together when we collaborate on materials. Share information, sources, prices, etc. Labor/OH/Profit we do have differing interests (we want more, you want less!), so compete this part.

Open Book Costing (we share too).

Transparency in cost is the heart of a should cost partnership. Finding a contract manufacturer willing to provide open book costing is a foundation to cooperating on reducing costs, especially materials cost. We provide you the line item detail necessary to understand your product cost so we can work together to drive it as low as possible.

It's a big world; prices will vary.

Global component pricing is an ever changing riddle. Since our management team includes a former distibution executive we have a clear understanding of how component pricing really works. One of the fundamental problems is component pricing is often silo'd inside the component suppliers. There is a nice person who prices United States procurements, a nice person who prices Asia, and another nice person who prices Europe. And they don't talk to each other. We often wonder if they even know each other, considering how widely prices can vary by global region. As a broad average, we believe component prices vary by about 20% around the world.

Global component sourcing

Savvy buyers must know which region of the world is currently pricing their commodities the best, so that's what we do for you. We maintain a network of sources that allow us access to sourcing around the globe. This is often very sensitive, so we work closely with you to make sure any existing domestic supply chain relationships are honored.

Cost reduction is an on going process, not an annual event.

World class outsourcing OEM's don't treat cost reduction as a yearly excercise, or something that happens during NPI, or as anything else special. It is part of their daily DNA. To get your best possible cost, you need a partner with a culture of cost reduction who works in cooperation with you to drive cost all year long.

Customized cost report

Our cost analysis process collects a lot of data and you will likely only want to see part of it. All of our cost analysis reporting is custom formatted for your needs in Excel. We can provide whatever you can use, here's an example of how one customer likes to receive the data.

Step 4: Lean Front Office Processing

Front office processing refers to those steps we take to import your BOM, acquire your materials, and bring your documentation into our systems. Once you release your order, our front office processes begin. The steps we take here are crucial to delivering your product on time and have a substantial impact on quality by reducing common errors. In this section you'll learn about surprising process innovations we have made through the application of lean principles to office processes.

Lean Insight #1 - All powerful Program Managers.

Our Program Managers run the show. They are not only responsible for satisfying your requirements, they have the authority to make it happen. Your Program Manager inputs your BOM, orders your fabs, communicates your specifications to Manufacturing Engineering, controls your documents, and plans the floor. Every one in the building follows the lead of your Program Manager. We do this because in a service relationship the most important value is delivered at the point of contact with the customer. Being outstanding in a service industry like contract manufacturing is all about enabling and supporting the members of our team in direct contact with you.

Lean Insight #2 - Dual BOM's.

We know, this is heresy, but it's phenomenally successful. We use your BOM in our costing tool for the ERP import which drives material and planning (see 'instant BOM import' below to understand why) and we pass your original documents to Manufacturing Engineering which uses them for programming the manufacturing equipment. The two BOM's meet at the kitting/feeder set up stage when the Picklist gets matched up with the Traveller. This is not only much more efficient, it creates a closed loop feedback channel that automatically double checks for simple errors, like data entry.

Lean Insight #3 - No dedicated document control function.

More heresy. It turns out Program Managers and Manufacturing Engineers, who actually use the data, are the most efficient and effective at storing it. To be clear, we have strong doc control practices, we just don't accomplish the task by passing the docs to a 3rd party for storage and access. Turns out that doesn't add value, in fact it induces error, and lean principles demand we eliminate such steps.

Instant BOM import

During the cost analysis process we collected and organized all the data necessary to import your BOM. In the process we identified and resolved any issue that would prevent us from importing, like missing, incorrect, or mis-matching information. We accomplished the myriad little things, like customizing your part numbers to our nomenclature, adding vendor codes, adding package codes, etc. Because this was all done very early, once we receive your order we simply hit a button and your data is instantly imported into our ERP.

Instant 100% ERP accuracy

We're really very pleased with ourselves about this one. Items are at the core of all ERP systems. Items have many fields, usually around 25 that matter. Typical active contract manufacturing divisions have 10,000-20,000 active part numbers. That's 250,000 or more fields that have to be correct. We don't know of any other company that has the tools to make sure all the fields are correctly populated, but if they did they would have 25,000 or more errors to correct (we know because we've done studies on these types of databases). We have built just such a tool and we know the moment your BOM is imported if there is any missing or out of parameter data. We believe we have the only ERP database in the industry that is 100% correctly populated 100% of the time.

Instant procurement visibility

We have aligned our internal procedures to allow any procurement or program management personnel to run ERP on the fly. Our ERP recalculates in about 15 seconds. So when your new requirements are loaded, purchasing sees them immediately.

Instant = Efficient = Low Cost

It's great that w can execute these processes instantly. But speed isn't the real advantage, it's cost. Fast means we are extremely efficient, and less time directly translates into less cost.

The industries best real time dashboard

The screenshot below is a portion of our in house developed real time dashboard. It is connected in real time to over 50 database components of our ERP and Quality Execution systems, interogating the status of about 100 key operational metrics. In addition, we push key parts of the dashboard to our smartphones 3 times a day, so we are always aware of our operational status. This creates another remarkable efficiency effect. Our team doesn't have to stop and think about what to do next, the dashboard guides them. And because each department stays on top of their metrics, there is little need to cross expedite each other.

Real Time KPI Dashboard
Update pushed to phones 3 times a day

Step 5: Manufacturing

Manufacturing defects are more commonly induced by human error than machine failure. So we trust automated processes, and double-triple check anything a human does. This simple philsosophy is the heart of how we approach manufacturing and achieve less than 25 solder joint DPMO.

Double Check #1 - Manufacturing Engineering starts fresh.

Manufacturing engineers start with the original customer documents to create the files and documentation necessary to process the job. Additional information to process the job is passed from the Program Manager to Manufacturing Engineering via an internal checklist to ensure all the required docs and data are present for engineering. We ask a lot of our manufacturing engineers. They basically start with fresh eyes and review the entire job in detail.

Double Check #2 - BOM compare at kitting.

At kitting we compare the Picklist BOM to the Traveler BOM. The Picklist is generated by our ERP and drives material. The Traveler is generated independently by manufacturing engineering. By cross-checking at this stage we verify correct BOM entry, including internal part number, quantity per, and AVL manufacturer part number, and packages.

Then we set up the feeders.

Ah, feeders. OEM's seldom realize it, but a contract manufacturer's investment in feeders can equal or even exceed the investment in SMT equipment. If you want to ask a savvy question next time you visit a PCB assembly operation, inquire as to how many feeders they have. You're probably looking for an answer of about 200 feeders per line. They need enough feeders to have each line running and a set up waiting for each line. If you want to know if they have enough feeders for your work, count how many SMT parts are in your largest BOM, times that by two, then times that by the number of SMT lines at the contract manufacturer, and that's how many feeders you need them to have (actually you should perform this calculation on the contract manufacturers largest build but for good reasons that's hard to know).

Double check #3 - Now we do a full audit.

Nowhere is our distrust of humans more evident. After the job is completely set up and ready to go down the line, we have independent quality auditors run a complete audit of the kit and set up. We actually remove a part from each feeder and not only verify it's the correct part number and package, we electrically verify the value of all passive components. Crazy, right? Here's what our audit looks like, those are physical components taped to each line item, and the physical model is generated from Valor:

Post Feeder Setup QA
Meanwhile, we're programming the equipment

This is another area we have eliminated a human step. We run your information through Valor to check for potential manufacturing problems, then we use Valor directly to program our equipment (most contract manufacturers use the equipment vendors software to program, meaning up to 4 different software packages to cover SPI, SMT, AOI, and AXI programming).We work very closely with Valor and the equipment manufacturers to support, streamline, and optimize this process. About 75% of programming time is related to developing a library of components for each equipment supplier. By working to integrate Valor libraries with equipment libraries we are pioneering an effort to greatly reduce programming time and improve optimization quality (this is a really big deal!).

Our SMT line capacity is up to 4x the industry average.

The capacity of SMT lines is expressed in component placements per hour (CPH). CPH ratings can be taken from manufacturer max rating, from an IPC standard rating, or from actual boards. The rating from actual boards is the only one worth paying attention to, and is derived from programming simulations of actual boards and verified with actual results down the line. Most industry SMT lines run two pick & place machines and have an actual CPH of about 15,000. We deploy a line with two Universal Instrument Fuzion machines, the line capacity is 60,000 CPH actual. Our other line deploys 3 Universal Advantis machines with a line capacity of 27,000 CPH actual. Put another way, we have the capacity of a 4 line SMT operation with half the overhead...more cost savings passed to you.

The secret sauce: Printing & Oven...

The manufacturing steps down an SMT line are solder paste printing, SMT placement, solder reflow oven, and wash. Of defects induced on a SMT manufacturing line, substantially all of them are related to either solder paste or the reflow oven. Exactly how we develop our printing processes and oven profiles is proprietary, but there are a few best practices we can share...

...solder paste printing best practices.

60-70% of SMT manufacturing defects can be traced back to paste printing. Keys to successful printing are selecting the most optimal paste and the best tools (stencil and squeegee blade). Solder paste consists of solder powder and liquid flux. The solder powder is comprised of metal alloys chosen for the specific application. The particle size of the solder powder varies, and the needle that dispenses the paste must be sized accordingly. The table below is best practice starting point for selection of solder paste/needle size combinations:

Dispensing Needle Size Selection Guide

For typical projects that contain fine pitch components we consider laser-cut stencils with micro-etching to be best practice. Laser cut stencils are made directly from CAD data which improves process control and can produce aperture widths as small as 0.004 witn an accuracy of 0.0005. When appropriate, laser cutting can produce tapered apertures, an angle of about 2° is best practice for optimal solder paste release.

...and oven profile best practices.

There are two approaches to oven profiles, ramp-to-spike profiles (also called ramp-to-peak or tent profile) and the soak profile. We utilize soak profiles on 9 zone ovens. There are four basic stages, preheat, pre-reflow, reflow, and cooling. During pre-heat the assembly's temperature is raised from ambient to a target temperature at a rate that can vary from 0.5 to 2.0°C per second. About 0.78°C per second is a good baseline best practice for average board sizes and densities. As the board moves between zones, a ?T (delta T) of =40°C is best practice. At pre-reflow, also called the "soak" phase, the goal is to bring the entire board to exactly the same temperature everywhere across the assembly. During this phase the component leads are prepared for bonding with solder by the flux activator, which removes surface oxide. The soak phase is critical to preventing voiding in all its forms, and is especially critical for hidden lead packages (BGA, LGA, QFN, etc.). At the reflow phase, the temperature of the assembly is raised just high enough to cause the solder to liquefy (the liquidus) and form a metallic bond with the component leads. Best practices are to raise the assembly's peak temperature to 20-30°C above liquidus and hold it there for a TAL (time-above-liquidus) of 30-90 seconds. During the cooling phase the objective is rapid cooling, because rapid cooling produces the most reliable long term solder joint by inducing a fine grain structure in the solidifying solder. However, if the cooling is too rapid solder joints will crack from thermal stress caused by different coefficients of thermal expansion between the component leads and the solder. Best practice is a cooling rate of 4°C per second.

Post reflow first article inspection

Once the first assembly completes reflow, the line is stopped while independent quality auditors verify the process. The assembly is first visually inspected, then undergoes automated optical inspection (our latest AOI was installed in 2014 and is state-of-the-art). When needed we inspect the board with automated x-ray inspection (our latest AXI was also installed in 2014). When these steps are complete, the board undergoes a final visual inspection, then the line resumes production.


As this overview demonstrates, the Optimum Method is not about tips & tricks; it's a consistant process that covers a range of disciplines and is designed to lower your cost while improving your quality. We don't know any simpler, more effective methods of saving you time and money.

What to do next

If you'd just like to learn more

We have tons of helpful information published on our blog. Here are some of our most popular articles to get you started:

If you're ready to consider using us now

If you'd rather find out now how we can save you money and improve your quality, just get in touch with us. We'll discuss if we're a good fit for each other and what next steps make the most sense

We know it's hard to select a new EMS partner, so here's how we've
made it easy and risk free.

As this overview demonstrates, the Optimum Method is not about tips & tricks; it's a consistent process that covers a range of disciplines and is designed to lower your cost while improving your quality. We don't know any simpler, more effective methods of

Step 1: You contact us, letting us know how we can help.

We'll get back to you right away and let you know what data we'll need.

Step 2: We analyze your data

To identify whether we're a good fit for each other. We do this because we don't want to waste each others time if we can't seriously help you. If the fit looks good, we'll do a cost evaluation and send it to you. After reviewing our cost data, you must be confident that we're on track to get you amazing results before we proceed.

Step 3: If you like our prices

We make evaluating us further a breeze. You can review our financials on demand (read what Circuits Assembly says about our financial disclosure). Your quality team can review a 60 page IPC audit report at any time. We'll encourage you to speak with existing customers so you can get a feel for what it's like working with us. Our state of the art Quality Execution System is fully on line and easy to show via a Webex. And when you're ready, we'll fly a team to your site to meet you personally.

Contact us now. You'll receive a FREE cost analysis and product life cycle report. No risk. No obligation. So why wait? Contact us now.