Determining Plated-Thru-Hole Sizes

 When designing your footprints, it’s critical that the size of the plated-thru-holes and their associated pads be sized correctly. Making these the correct size will help make sure there are no issues assembling your PCB’s. After all, you’ve likely spent many thousands of dollars to get this done and the delays that might be introduced by something as simple as a bad hole size can be a real bummer.

There are 4 steps to designing your PTH correctly.

  1. Determine the density of your design

  2. Determine the lead diameter

  3. Determine the plate-thru-hole diameter

  4. Determine the pad diameter

1. Determining the Density of Your Design

The IPC organization suggests three different density levels in your design process.

  1. Density A (least dense, easiest to manufacture)

  2. Density B (moderately dense, moderately easy to manufacture)

  3. Density C (most dense, most difficult to manufacture)

Give some thought to how densely populated your assembly will end up being. With this information in mind, you can determine your overall hole sizes and pad diameters, which we’ll cover in steps 2-4

2. Determine the Lead Diameter

This is an easy one. Take a look at the datasheet for the part you’re using and find the diameter of the lead. If the lead is rectangular, then use the dimension from the two opposite corners.

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3. Determine the Plated-Thru-Hole Diameter

IPC suggests that you can take the lead diameter, add a certain value to it, and this will end up being your plated-thru-hole diameter. For Density A, this extra margin is 0.25mm. So if your lead diameter was 0.5mm then your plated-thru-hole would be 0.75mm diameter.

Presentation2.png

4. Determining the Pad Diameter

IPC suggests that you can take the hole size, add the minimum annular ring size, and then add some extra margin to determine your pad size. A typical minimum annular ring is usually 0.05mm. So if you take that 0.05mm, add to it 0.3mm, double that number, and then add it to the hole size, you’ll come up with your pad diameter.

In our example above of a 0.5mm lead diameter and a 0.75mm hole size, our pad diameter would end up being (0.05mm + 0.3mm) x 2, then add the 0.75mm hole size and you get 1.45mm

Presentation3.png

We hope you found this information helpful. As always, if you have any questions, please don’t hesitate to reach out.

How Does Chinese New Year Affect Electronics Manufacturing

Chinese New Year 2019

Monday January 28th – Tuesday February 19th

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Short Version

Chinese New Year will affect the delivery of your assemblies. Unexpected delays will occur. If you have not already placed your order for assemblies, then it’s almost guaranteed that your delivery will be impacted by CNY. If you really need your assemblies before CNY then you can pay to have your order expedited but that’s still no guarantee that your order won’t be impacted by CNY. The earlier you place your order though, the better the chance of getting your assemblies on time.

We usually do not see things get back to normal with deliveries until nearly 1 month after the end of CNY.

Long Version

China’s Spring Festival, often referred to as Chinese New Year, is an annual event usually held somewhere around the end of January to mid-February. While it’s probably a time of enjoyment and celebration for the people of China, it’s usually a time of great stress and frustration for the manufacturers that rely on China’s great manufacturing supply chain.

As a manufacturer based in the United States you might think we are insulated from this holiday. However, the truth is that no matter where your product is made, China is likely somehow involved in the supply chain that ends up being a part of your final product. But even if they somehow aren’t (they most likely are) their shutdown will still have an impact on the delivery of your product.

The world only has just so much capacity to manufacture things. China has the largest portion of that capacity. So when they shut down just about their entire manufacturing operation, this is going to have some impact on the rest of the global supply chain. Manufacturers in the United States are going to see their orders increase substantially. But even with working overtime and weekends, they could never dream of compensating for the total loss of production in China.

When China stops accepting orders at the beginning of CNY, demand for product, and thus orders for goods, does not slow down. So orders to domestic manufacturers see a large increase. Their peak capacity will be reached very quickly, especially considering every manufacturer in the United States is already running a lean shop at very near peak capacity. So when they see orders increase, lead-times start to get extended.

One of the primary goods that we order from China is bare PCB’s. During their shut down, our customers continue to order assemblies. Once our board suppliers get back to work, they are going to have an enormous backlog of orders from being away for 2 weeks. It will take them a long time to work through that backlog. So even though CNY is only a couple weeks, this does not mean that orders placed during CNY will begin shipping right away after the end of CNY. We usually do not see things get back to normal with deliveries until nearly 1 month after the end of CNY.

While our friends on the other side of the Earth are getting some well deserved time off to see their family and enjoy their holiday, the rest of us will do our best to keep customers informed about how this holiday will impact their supply chain, and do our best to handle the flood of material that hits us once the material begins to ship to us again.

As always, if you have any questions, we’d love to hear from you.

The Perfect 0201 Footprint

A while back 0402's were a huge pain in the neck. The primary issue with them was honestly footprint design. Pick and place was more than accurate enough but we still kept running into design issues. Because we saw such an enormous variety of 0402 footprints here, we decided to write an article called "The Perfect 0402 Footprint". It was very well received and ever since we published it, we've seen very few poorly designed 0402 footprints anymore.

Fast forward a few years and the 0201 is the new 0402. We keep seeing a number of head-in-pillow and tombstone defects with these. These images are of an 0402 but the defects are effectively the same.

This is what a "Head-In-Pillow" defect looks like. Notice how the right side isn't actually wetted to the component.

This is what a "Head-In-Pillow" defect looks like. Notice how the right side isn't actually wetted to the component.

This is what a "Tombstone" defect looks like. It might be hard to notice at first, but the pad on the left has the 0201 capacitor standing straight up in the air.

This is what a "Tombstone" defect looks like. It might be hard to notice at first, but the pad on the left has the 0201 capacitor standing straight up in the air.

So, just as we did with the Perfect 0402 Footprint, we're recommending what we consider to be the Perfect 0201 Footprint and are encouraging all of our customers to use it in their designs. 

The Perfect 0201 Footprint

The Perfect 0201 Footprint

The critical aspect of this design is the gap that remains between the two closest edges of the pads. This gap should be no more than 0.3mm. This is what helps to make sure that the terminals of the chip are definitely making contact with each pad. If the gap between the pads was any larger, even by just 0.1mm, then we begin to run into serious head-in-pillow and tombstoning issues.

We put together an EAGLE library for this part which you can download here.

This page will be linked in our Best Practices page for future reference.

If you ever have any questions, please feel free to reach out to us. We'd love to hear from you. My email is address is cdenney@worthingtonassembly.com and our phone number is (413) 624-6879.

Dragon Innovation's Product Planner

We get it, BOM's are boring. Nobody's changing the world with a BOM. But BOMs really are the life blood of almost any product. A considerable amount of effort put into a BOM will save you countless hours and money when coordinating with manufacturing, and even to determine whether or not you can make any money with your product. As the founder of Dragon Innovation, Scott Miller, likes to say "Early decisions cast long shadows."

Recently we got to spend some time with the folks at Dragon Innovation and they gave us a great demonstration of their Product Planner software. I really liked what I saw and wanted to take some time to point out why I think software like this is important, and how it can be valuable to you when you begin working with a manufacturer. 

dragon logo stacked.png

Dragon themselves have a nice concise way of describing what Product Planner is...

Product Planner is more than a BOM management tool. It gives you the insights you need from your BOM to gain confidence that you are on the path to manufacturing success. It’s also a gateway to fast-tracking your progress via Dragon’s expertise.

Getting Started

You get started with Product Planner but uploading your BOM. It's a typical interface you've seen before for uploading anything to the web. Drag-and-drop your CSV to get started.

Once you have uploaded your BOM, Dragon takes it from there and crunches some numbers on it. They say this takes a few days to complete.

Thankfully, you don't need to wait that long to play with Product Planner. Right away they set you up with a Demo project so that you can get a feel for how the software works. 

Within the first few moments of using Product Planner, Dragon presents a very nice analogy for what goes into making a product. It's often far more than we think. There are many parts that go into making a product, and the two should not be confused.

The computer on the left represents all the work you put into the product. The smiley meal on the right represents the fruits of your labor. Most people would think that the BOM for this product would be a burger, fries, and a box. But it's so much more than that, and their next slide does an excellent job of breaking that down.

You see, even just the burger itself has so many different parts that need to be considered. And then within each of those parts are other parts. For instance the meat itself isn't just meat. It has onions and spices in there. The same goes for your PCBA. You can't think of it as just a single part number. There are dozens, sometimes hundreds or even thousands of other components that need to be populated onto the PCB that you need to consider.

And of course it doesn't stop there. There's the packages, the accessories, the napkin, the box, etc. There's a lot going on with every single product. If you don't take the time to think about all of these details, you may catch yourself in a position where your project is out of control, you cannot meat your deadlines (see what I did there?) and ultimately you could end up losing money for a long time, or worse still, never make any money at all.

Once you've got your data entered, you'll see how rich the software is. There are so many bells and whistles to this thing but yet I never felt overwhelmed by it. The user interface design is very nice. Buttons are either clearly labeled or their icons are so obvious as to what they do that you never feel lost. Each button has a comment box that appears when you hover over the button too, in case you forget what its utility is.

BOM View

You'll likely spend a considerable amount of time in the BOM page. There are 2 different ways you can view your product here, either Indented View or Flat View. These show you all of the various parts of your BOM in a super clean and efficient manner. I really like it.

Indented View

Flat View

I prefer this indented BOM view. It really helps you to see the overall scope of the product and how each part fits into it. This visual representation of BOM's has always reminded me of those Russian Nested Dolls. 

You can then drill into each item of the BOM to view and/or edit specific details related to that part.

Parts View

All of the various fields here that can be filled out will really help you to think about the details of your project. For instance, is this the kind of part that can be purchased "off-the-shelf" or will you need it custom made, just for you? Have you thought about your unit costs vs. your fixed costs? Whats the typical lead-time to get this part fabricated? What suppliers are lined up to produce these for you. There's an area where you can insert an image of the part which is quite handy because we humans are a visual bunch. Having an image of the part under consideration is very helpful. They also have a handy area where you can upload various files related to that part. This would be a great place to put things like CAD files, schematics, drawings, etc.

Whenever we've done completely fulfillment for customers, we inevitably have to have a conversation with them about how the product is going to be presented. Will there be a box this goes into, or just a bag? Will there be a user manual, stickers, labels? What about cables and other accessories? Product Planner helps you think about all of those things. When you click the Add Part button, you'll be presented with a series of boxes to choose what type of part you want to add. Simply the act of presenting these options to users forces them to think about the details. "New Packaging" part will remind them "Oh yeah. This thing has to be presented to a customer somehow." I know it sounds trivial, but you would be surprised how often major details like this get overlooked.

Having to fill out all of these fields will really help you when it comes time to work with a manufacturer. You'll know what questions to ask and what information to present. All your i's will be dotted and all your t's will be crossed and your supplier will be grateful for it. The more thoroughly documented you are, the less questions will come up, and the smoother and faster your parts will come in.

Reports

But I think by far where most people will find Product Planner beneficial for their company, is the reports area. These reports can give you such incredibly valuable insight into your product that would otherwise be obfuscated by the complexity of the project itself.

Take for example one of the most powerful reports, the Break-Even Report. This report is exactly what it sounds like. At what quantity and at what dollar value will you finally start making any money. Your revenue needs to go up faster than your COGS (cost of goods). If it's not, then you've discovered a very useful way of wasting a lot of money.

In this report you can select your product SKU, enter your product price, and see the graph change right before your eyes. If you find that your retail price is so low that you'll never make any money, then you can easily change it to see where you can start making money. Of course it's not always that easy to just start charging customers more. So something in your COGS needs to change. For that, they've got plenty of other valuable reports.

For example, the High Cost Parts Report is a beautiful presentation of the most expensive parts in your BOM. You can easily see where most of your money is going to and it can help you identify where you might possibly reduce some of your COGS. 

The way this information is presented is actually quite beautiful. It reminds me a lot of those utilities that help you find files that are occupying the most space on your computer hard drive. The colors used are also quite attractive and has sufficient contrast that you can easily identify the different parts.

I also really like the Fixed Cost Breakdown Report. Here you can quickly see the cost of things that won't be repeated per product fulfillment. The visual presentation is similar to that of the COGS but having these NRE's broken out this way is helpful to see whether or not you might be able to bring that break even number down a little bit.

Crystal Ball

It's nice to see that a product like this finally exists. A thoroughly vetted and reviewed bill of materials can be like using a crystal ball to predict the future. Even just presenting questions about important details such as packaging and labeling can really help keep your project moving forward. Your suppliers will be grateful because you will be more prepared. Being prepared can save you time and money. If a supplier can tell that you have not really thought about your project thoroughly enough, then they may be less willing to offer you favorable payment terms or even take your business at all. They need to get paid too, and if they're worried that you don't have a plan, then they might not be willing to take on the risk of working with you.

The difference between a successful product and an unsuccessful product often comes down to how well you have planned. As a friend of mine used to say "A goal without a plan is just a dream." Have a goal, put together a plan, execute it, and enjoy the process. Surround yourself with good people, and give them good tools like Product Planner, and then maybe, just maybe, you'll be successful too.

Digikey Rolls Out Reverse Part Attribute Lookup

I'm going to dump some praise on Digikey for a moment. These people rock.

In addition to having the fastest site of all part distributors, the cleanest presentation of their database, the most helpful product attribute table in the business, the fastest fulfillment service, and on and on, today they released what I'm calling Reverse Part Attribute Lookup. First, let me explain the problem that they solved.

Each day, we are introducing dozens to hundreds of new components to our process. Each of those components needs to be in stock and ready to buy to make sure we can build the order for our customer. But sometimes, our customers specify parts that are either not in stock, have the wrong package size (0603 instead of 0402, etc.), have the wrong orientation (right angle LED instead of vertical, etc) or some other weird thing that makes it unusable. So very often we need to find an alternate part number that will work for their design. Here's an example.

Let's say a customer specified an 10k resistor with a 5% tolerance, and in an 0402 package, like RC0402JR-0710KL. But their design calls for an 0603 footprint. Well the process we formerly went through to find an alternative would be to go to Digikey's Product Index, then choose Chip Resistors, and then click one by one, each filter we were interested in at the top of the page. In this case 10k for Resistance, 5% for tolerance. Then we would check the box for "In Stock" and click Apply Filters. 

That doesn't sound too bad, until you have to do it over and over, many times each day. Additionally, there are other attributes which may or may not be important. Power Rating, Composition, Temperature Coefficient, etc. It can take time to look back at the original part number specified and scroll through a huge list of options for each attribute.

For years (not exaggerating, literally years) I have wanted a tool to tell me what other part numbers exist that match all of the same attributes as the part number I'm currently looking at. Basically a Cross Reference tool. But I'd like the ability to change just one attribute, like the package size (0603 instead of 0402). Well, those beautiful nerds over at Digikey did it. They have given us a dream of a tool.

First, pull up a product page. We'll use RC0402JR-0710KL for our example. You'll notice now in their Product Attributes table there are check boxes next to each Attribute. As you click these check boxes, you'll notice their software automatically tell you how many other parts match these attributes. As you keep clicking the number of parts that match will keep falling, based on how many other parts match it, until you finally have a nice clean list that you can easily sort through. 

Here's a quick demo so you can see it in action.

This is so much easier than the old method we used to use. It saves time yes, but it also reduces the risk of recommending the wrong alternate part number. Thank you Digikey for making this. Thank you! Thank you! Thank you! 

PS - If an executive gets their eyes on this, maybe they should buy their team some pizza ;)

Your friend
-Chris

You’ll be malfunctioning within a day, you nearsighted scrap pile.

We do a lot of cool things here at Worthington Assembly. Some of them cooler than others. And as every typical American kid raised in the 80's, I've been a huge fan of Star Wars my whole life. So needless to say I was super excited when Paul Murphy of the R2 Builders Club reached out to us to build some assemblies for him.

Recently we had a chance to see Paul at Star Wars Night at a Boston Red Sox game. The reaction to his R2D2 unit was incredibly. More than a few kids ran up to give R2D2 a hug. I know I would have if I wasn't worried about Queen Amidala calling security on me.

It was exciting to see our work in real life. We assembled the Logic Display control boards for him. In his words "Logic Displays are the blinky lights in the rectangular openings of R2-D2's dome (2 front, 1 rear) that separate dead droids from the living". You can even see the "Assembled in Massachusetts" logo on the PCB.

Here's a video I shot showing Paul controlling his R2D2 unit from a distance before the Sox game.

You can learn more about his work by visiting is GitHub repository here

If we've built something for you and you would like us to blog about it, let us know. We love learning about what happens to the boards after they leave our factory.

How To Use CircuitHub

If you have ever wanted to try to use CircuitHub but weren't uncertain about the whole process, well there's good news. We've produced a short "how-to" video demonstrating CircuitHub. It will walk you through the whole process from importing your files, reconciling your part numbers, consigning material, choosing a board color, thickness, and copper weight, and finally hitting the buy button. We hope this will help new users get more familiar with the process and maybe existing users will learn something that they weren't aware of before.

Presentation At The Isenberg School Of Management

Over the past several months, WAi has been working with a smart group of MBA students from the Isenberg School of Management. It has been an enlightening and eye opening experience. We learned a lot and having them dig in and ask some tough questions got us to think about how we do things and helped us refine our process a bit. 

Their final presentation was today and we thought they did a great job so we wanted to share!

Working With A Manufacturer - The Best 0402 Footprint

So you've got a great idea and you want to bring it to market, but you don't know the first thing about hiring a manufacturer and working with them to get your product assembled? We are here to help. This is one piece in a series of articles that we'll be writing that will help people learn how to work with us to get their product assembled. 

We see a lot of different, unique assemblies come through our shop. On average we are introducing a new job to our factory every single day. This means the assembly has never been built by us and likely has never been built by anybody. With this amount of new work, we've seen the good, the bad, and the downright ugly when it comes to footprints.

The most sinister of all footprints is the 0402 footprint. There's something about the 0402 component that just loves to drive us insane! The issue is that many footprints inadvertently cause the component to "tombstone" or worse "head-in-pillow". Here's what those defects look like.

This is what a "Head-In-Pillow" defect looks like. Notice how the right side isn't actually wetted to the component.

This is what a "Head-In-Pillow" defect looks like. Notice how the right side isn't actually wetted to the component.

This is what a "Tombstone" defect looks like. It might be hard to notice at first, but the pad on the left has the 0402 capacitor standing straight up in the air.

This is what a "Tombstone" defect looks like. It might be hard to notice at first, but the pad on the left has the 0402 capacitor standing straight up in the air.

The biggest culprit of all 0402 issues is the default 0402 footprint in the Eagle library that comes with every installation of Eagle (I love Eagle. I really do. I just hate this one footprint). So, if you have 0402 components in your design, please, for the love of all that is honest and good in this world, change that 0402 footprint to the one we recommend. 

Here's a video showing me editing this footprint in Eagle.

The perfect 0402 Footprint

This video was made using the Eagle EDA tool. But here are the dimensions you'd want to use if you designed this in any other EDA tool.

The Perfect 0402 Footprint

The Perfect 0402 Footprint

We have populated hundreds of thousands (probably millions) of 0402's with this footprint. We've had such success with this footprint that I had to reach out to the engineer who designed this footprint originally and thank him for his design. He thought I was ridiculous because it was just the standard dimensions that he found on a datasheet many years ago. But the difference is he actually created his from scratch, rather than relying on the default footprint in his EDA tool's library. And this is the key. Whenever you start using a new footprint, please check it against a datasheet and make sure it matches. Your manufacturer will thank you.

If you ever have any questions, please feel free to reach out to us. We'd love to hear from you. My email is address is cdenney@worthingtonassembly.com and our phone number is (413) 624-6879.

Working With A Manufacturer - What Are Fiducials and Why Are They Useful?

So you've got a great idea and you want to bring it to market, but you don't know the first thing about hiring a manufacturer and working with them to get your product assembled? We are here to help. This is one piece in a series of articles that we'll be writing that will help people learn how to work with us to get their product assembled. 

We get this question all of the time. Many designers have no idea why they would put some random piece of copper on their board when it serves them absolutely no purpose.

Fiducials are reference points on the PCB for automated equipment. Its full name is "Fiducial Marker" and according to Wikipedia a Fiducial Marker is 

an object placed in the field of view of an imaging system which appears in the image produced, for use as a point of reference or a measure.

In other words, fiducials help machines recognize where an object is in its space. For PCB assembly this means that our stencil printing machine, pick and place machine, and AOI machine can recognize where the PCB is when it goes to perform its task.

We encourage customers to use 3 fiducials. If you can't fit 3 fiducials then 2 fiducials will generally suffice. But 3 fiducials is the best. Each one serves a purpose.

1st - The first fiducials helps the machine recognize where the PCB is in its space in the X and Y dimensions.

2nd - The second fiducial helps the machine recognize what orientation the PCB is in and also how skewed the PCB is in the clamps. If the PCB is rotated even 1/10th of a degree this could completely ruin the assembly if it weren't for fiducials. The machine is able to measure the angle that the board is rotated in the machine down to the nearest 1/100th of a degree and compensate all of the placements accordingly.

3rd - Finally, the third fiducials helps the machine compensate for any shrink or stretch of the PCB. Yes, believe it or not PCB's do vary by very small amounts over a long enough distance. This is very important for larger PCB's because they experience a much greater amount of stretch and/or shrink. This is especially true for double-sided SMT assemblies. After the first side is reflowed in the oven the board may have stretched, shrunk, bowed, flexed, whatever you want to call it. Having the third fiducials can help compensate for this effect.

The next question people ask is, well why stop at 3? Why not have a 4th? Well, imagine this scenario. Your PCB is placed inside the machine rotated 180 degrees. What happens when the machine goes to inspect the 3 fiducials? It will find your 4th fiducial and start populating the entire PCB thinking that it understands it orientation correctly. This has happened to us, more than once, by well meaning designers. So, for the sake of sanity and my ever growing collection of gray hairs, please only put 3 fiducials on the PCB.

Fiducials are necessary whenever SMT components are going to be placed onto a circuit board. This includes double-sided SMT assemblies. So make sure to put fiducials on both sides of the PCB because cameras can't see through circuit boards. It needs those fiducials on both sides.

So when you are designing your next PCB or revising and existing PCB, please consider adding fiducials to your design. Many designers have found that using a 1mm round fiducial with a 2mm masking area around it works best. This masking area eliminates any glare that might reflect into the camera from the glossy finish of the masking. The best placement of these fiducials would be at the corners of your PCB. Not all the way up to the edge. This could cause the clamps of the machines to cover the fiducials. Try keeping them about 5mm from the edge or so. You can probably squeeze them in as tightly as 3mm but that's cutting it close. 5mm leaves plenty of breathing room.

We have put together a nice document about automated PCB handling. You can download it by clicking here. Also check out our best practices page if you haven't already done so for other helpful information.

As always, if you have any questions, please do not hesitate to reach out to us. We'd love to hear from you. You can email me at cdenney@worthingtonassembly.com or give us a call at (413) 397-8260.