Final Surface Finish: How do you choose?

There are so many final surface finish options to choose from today, how do you decide which is best?  HASL – lead and lead –free, Immersion Tin, Immersion Silver, ENIG, OSP, and ENIPIG are the primary finishes used in PCB fabrication.  Fabricators and assemblers generally work with the majority of these surface finishes to be able to support their customer’s requirements.  So, the question is, with all of these available, how does an OEM select their preferred surface finish?

In the past, the primary function of the surface finish was to protect the copper from oxidation prior to the soldering of components.   Today’s expectations include:  superior solderability, contact performance, wire bondability, corrosion and thermal resistance, and extended end use life.  Designs have changed.  Lines and spaces are reduced, solder types and flux chemistries are different due to no lead requirements, the number of assembly cycles has increased and the product may need to carry high frequency signals.

Things to think about when selecting a final surface finish:

• Does the application require lead or lead-free assembly?
• Will the end environment have extreme temperatures or humidity concerns?
• What shelf life is needed? Will it be months or years?
• Volume and throughput
• Does the design have fine pitch components?
• How many assembly cycles will be required?
• Is this a RF or high frequency application?
• Will probeability be required for testing?
• Is thermal resistance required?

Once the project requirements have been identified, the surface finish options can be reviewed to find the best fit.

Click here for detailed information for each surface finish.

Tara Dunn, Omni PCB

A glimpse into PCB Sales

Here is a little sneak peek into the daily life of a PCB sales person.

Prospecting:

Somebody not in PCB sales might get a little laugh, but those of us in the trenches see this and and think, haha, is that me? Yes, it is! It is incredibly hard to get in touch with PCB buyers or designers and when someone answers the phone, we do a little happy dance. THEN if they don’t say “no, thanks”, we are SURE they will one day be a customer. We just have to be patient.

When a customer calls:

I know…..someone is reading this and thinking, “really? The PCB sales people I know like to take long lunches and spend their afternoon’s golfing. They don’t want to help me”. Old stereotypes are hard to overcome. But, I have been in PCB industry a very long time and have had the privilege to get to know many PCB sales people that are very good at what they do. In my opinion that is often because they truly enjoy getting to know their customers and helping to solve problems.

As I was thinking about what I wanted to say about PCB Sales in this column, I thought it would be both interesting and educational to ask both customers and manufacturers their thoughts on PCB Sales. I was pleasantly surprised at the enthusiastic response I received.

Question #1: In your opinion, what traits do good PCB sales people have in common?

From PCB Users:

* A better than average knowledge of PCB construction

* The ability to offer suggestions and solutions when we struggle with a new design and technology need

* Respond quickly when there is a request or issue

* Provide follow up to the details so I don’t have to worry about what is being completed

* Know the line between persistence and annoyance. PCB’s aren’t the only thing on my plate

* Excellent communication skills

* Understands when I call with an issue and helps work with manufacturing or engineering to resolve the issue so I can focus on other things

* Takes the time to learn how we prefer to work and customizes responses to fit as best as possible

* In depth knowledge of the PCB market, new materials, supply issues, etc. and provides information on what might be important to us

Got it: Knowledgeable about PCB’s and the industry, organized, strong communication skills and customer focused.

From PCB Manufacturers:

* Persistence and tenacity to follow thru and listen more than they talk

* In-depth understanding of the customer, how they like to work and what additional business is available

* Respond quickly and thoroughly

* Consistently find new opportunities and new business

* Great follow up, know their customers, aggressive when they need to be and very personable. Did I mention organized?

Got it: Knowledgeable about customer’s needs, organized, strong communication skills and brings in new business. These two lists are actually pretty similar.

Question #2: What do you wish PCB sales people did that they currently don’t, or currently don’t do well?

From PCB Users:

* Advocate for annual cost savings on behalf of the customer. This would foster trust and repeat business

* Understand our systems and market pressures outside of ordering the PCB. There are a lot of different considerations and decisions made that may not be apparent to the PCB manufacturer but are critical to us.

* Proactivity. Offer suggestions for cost or lead-time reductions. We are not the experts in PCB design and would be interested in how we can improve

* Provide the very best price the first time, especially with larger programs. Don’t come back with reduced pricing after I give you feedback. That wastes time and resources for both of us.

Got it: Detailed knowledge of customer’s business and proactively advocate for your customer’s best interest.

From PCB Manufacturer’s:

* Ask for the PO and know how to sell value, not just on price!

* Stop relying on price to differentiate and win the order

* Close more business in a timely manner

* Identify customers that find value in the quality, customer services, and fast response that we offer rather than sell on price.

Got it: Differentiate the manufacturer’s offering so the comparable factor between offers is not price alone. Interesting, this is similar to the message above also; advocate for value of the manufacturer’s strengths with your customers.

Summarizing the feedback from both customers and manufacturer’s, the most successful sales PCB sales people are organized, take a genuine interest in their customer’s needs and business challenges, have a better than average understanding of the PCB industry, fully understand the manufacturer’s strengths and capabilities and have the ability to advocate for both to find the best solution. There is room for improvement by being more proactive in solving your customer’s challenges and in understanding the differentiating value of the manufacturer to sell on total value rather than price.

You will get all you want in life if you help enough other people get what they want. – Zig Ziglar

My closing thought is that it truly is difficult to reach a comprehensive level of understanding of both the customer’s needs and the needs of PCB manufacturing. The information that is easily obtained, is often just skimming the surface of the full picture. Sales people continuously search out opportunities to interact with their customers outside of the conference room. Those relaxed conversations often offer the best glimpses into what people really need from their sales person. There is no roadmap to use, every customer has different needs. If you attend an IPC show, SMTA expo, IPC Designers Council meetings or even Geek-A-Palooza, there is no shortage of sales people trying to increase their technical knowledge and get to know others. I strongly encourage PCB users and PCB manufacturers to do the same. The more we all know about each other’s needs, the stronger the relationships will be for everyone.

Troubleshooting Flex Applications

I imagine that everyone has been in this position at one time or another, despite everyone’s best attempt at creating the perfect design, PCB fabrication and assembly, something goes wrong and the trouble shooting begins.  I had the opportunity to sit down with Ed Knutson, the President/Founder of Dimation, to swap some of our best war stories.  Ed specializes in quick turn assembly and design and I bring the fabrication piece to the discussion.  Our banter back and forth was primarily focused on flexible circuit applications for aircraft and Mil/Aero projects.  I am not sure if that is because of the more stringent requirements for those applications or more likely because that is an industry segment that we both work with regularly.   At the end of our discussion, we concluded that most of the war stories could be traced back to a break-down in communication and often times simply not fully understanding how each piece of the design-fabrication- assembly puzzle fit together.  We want to share a few of our stories and lessons learned.

UL Materials

Aircraft applications typically require materials rated to UL94V-0.  The assembly is complete and the burn test fails.  What happened?  The perfect storm.  When the design files were created for the PCB fabrication and assembly, the UL requirements were noted in the assembly files only and called out by test requirements, not UL 94V-0.  This was an ITAR application, so the PCB fab files were separated from the assembly files and forwarded the flex manufacturer.  Because there were no UL requirements listed on the fabrication notes, the supplier defaulted to their standard materials and the flex was not built with flame retardant materials.  That explains why the final assembly failed the burn test.  Lesson Learned:  Always clearly communicate UL requirements and include the requirement in both the PCB fabrication notes and the assembly notes.

Coverlay

There were many stories along this line, but this one is classic, we have both seen this more than once.  A particular application, on a tiny flex circuit, requires a very tight pad pattern. Standard, adhesive based coverlay, was called out in the stack up.  As the flex manufacturer was setting up the tooling, they asked if that area could be “gang opened” because the tight features would cause fabrication issues when aligning the drilled coverlay.   That is a very common question that I have seen asked and approved hundreds of times.  The designer agreed that would be fine and that pad location was left free of coverlay.  But, once the parts arrived at the assembler and they went to screen print the paste, the area shorted out.  The problem was ultimately solved by using photimageble coverlay to accommodate the tight feature pattern.  Lesson Learned:  Review even the “standard” requests with a critical eye for the next processing steps the flex will see after fabrication.   The size of this particular flex combined with the tight features was the perfect combination to cause an issue with something that is routinely done.

Bend radius

By definition, flexible circuits are designed to bend, fold, and flex during installation and/or use.  That doesn’t mean that the copper will not crack or break when it is overly stressed.  There are two very important things to be aware of.  First, RA (rolled annealed) copper versus ED (electodeposited) copper.  There really is a significant difference in ductility.  With a tight bend radius, or for a dynamically flexing application, specify RA copper.  Second, involve your fabricator.  The flex manufacturer is only going to see the design in a two dimensional view.  They will not know exactly how this is going to be used in your final assembly.  If you are concerned about bend radius or otherwise stressing the copper, ask for their advice.  There are many different “tricks of the trade” that a flex fabricator can recommend to ease the stress on the copper and improve performance.  Use their knowledge!

Array configuration for assembly

It is common knowledge that assembling flex can create challenges.  A lot of trial and error is done to find the best way to handle it.  Flex circuit size, array configuration, component placement and stiffener requirements all play into the decision, which just may be equal parts art and science.  The first decision is whether the assembly will be done by hand or machine.  If the assembly is not done by hand, whether to use a stiffened array or machined pallet needs to be determined.  Here are a few examples:

For a small flex, with a few components on just one side and no stiffener requirements, consider creating a FR4 stiffener pallet with adhesive on the outside perimeter only.  After assembly, the flex can easily be peeled away from the stiffener pallet.  Caution:  a stiffener pallet with adhesive in selected areas only can easily be misunderstood during fabrication.  Make the objective very clear in the fabrication files.

For a long flex with stiffeners, we suggest cross hatching the copper, or adding in a copper pattern to maintain as much of the copper in the array as possible to add stability.  The flex can be pre-routed with tabs left to hold this into the array during assembly.  Once parts have been assembled, simply cut the tabs to release the flex from the array.  Caution:  stencil tolerance over this long length is an issue to be aware of.

A custom pallet is another common choice for assembly, especially when you are running more than a few panels.  Most often this is designed with FR4 material. The benefit to this is stability and flatness during assembly and also the ability to nest the flexible circuits in the tightest configuration possible to reduce the cost of the fabrication.  There is no need to add in extra copper area in the array for stability.

These are just a few of the lessons learned that we have accumulated over time.  I hope that these provide insight and suggestion that will help with your future flex designs, or at the very least, let you commiserate and know that you are not the only one challenged with these types of issues.  Feel free to get in touch and share your stories with us!