Kitted vs. Turn-key assembly

Which is right for you?

If you're familiar with us, you probably well know what a kitted job is. Most of our orders come in that way. For those of you new to Screaming Circuits:

A kitted job is where you send us your files, all the parts and the empty pc boards. It's the easiest way to go. You quote the assembly only on our handy quote page - that will show you exactly what it's going to cost. Shipping is extra and if you need any non-standard or special services, they will be extra. But, for the vast majority of jobs, what you see in the on line quote is what you pay for the job.

Quote it, answer a few more questions, up load your files and ship us the kit. If everything is in order, we'll start your turn-time clock  then morning we get your kit. (check out our terms for exact information).

Turn-key:

The turn-key is easier for you all around, but the quote process is a bit more awkward.

We like you to go through the labor quote process first, just like for a kitted job. Then go ahead and place the order but in the special instructions, clearly note that this is for a turn-key quote and not a kitted order. We'll give you a call, work out all the details and get back to you with a full quote in about a day.

Duane Benson
I need a latte

Random PCB Assembly Questions

We have a lot of information on our website. Hopefully it's mostly all useful by somebody, but even if it is, there's still a lot to wade through just to find the two or three factoids you are looking for. Sometimes I can't even find what I'm looking for. We do have the little search box up in the top right, but it doesn't always work like you would think.

For example: we received an email the other day asking what kind of flux we use for lead free. (We use no clean) I know that we use no clean solder and solder paste, but just for kicks, I put the word "flux" into the search box. I got nothin.

On our capabilities page, we do say that we use "no-clean" but we say it in reference to solder type, not flux. As far as I could see, we didn't use the word "flux" anywhere on our web site. Well, that's not so smart. Somebody want to fix that for me?

Duane Benson
Must flux website

Bent SMT pins

Protect those pins!

It's nice to be flexible, right? We know that most of you like to order parts in cut strips to save money, or you have a short strip left over from a prior job. That's cool. We're all about saving money and not wasting parts. In fact, we like that a lot.

Sometimes, though the old parts drawer doesn't do us (or you) any favors. We recently ran across a small strip of QFPs in a kit. Normally, a set of three in the original strip wouldn't be a problem. In this case, though, they had likely gotten just a bit too friendly with some of the other parts. Or maybe they had gotten into a fight or something.

All three parts had a substantial number of bent pins. In cases like this, we'll look at the chips and see if we can straighten them, but we can't always do that. Sometimes we have to call and ask you to send more parts and delay the job, which is a bummer all around.

When kitting up a job, give components like this a quick look over. When you're storing extras for future use, make sure to keep the sensitive bendy parts like this away from big and heavy things.

Duane Benson
Always one more thing to check, huh?

Spotlight: The Centroid File

We recieve a lot of questions about the Centroid file that we require. The file just tells our machine where each part goes on the board and what direction to point the part when putting it on the board. It's not the only file we need, but it is certainly one of the most important.

There are two ways that we can end up with a good Centroid file; a) you can provide it, or b) we can generate it from the other CAD and BOM files that you provide. If you want us to make it, we'll charge $50.00 to $100.00 for a typical board, sometimes more for really complex boards.

Most CAD systems will automatically output the file for you. It might also be called an "Insertion file", a "pick and place file" or an "X-Y file."

If you use:

• PCB123: If you use PCB123 and tell them that you are sending the boards to Screaming Circuits, they will send us the Gerbers and Centroid without an extra charge.
• Eagle: Download the User Language Program (ULP), described here on our web site, and run it on your board.

If you want to create it yourself, of just understand it better, download our PDF describing it and our sample Centroid file from our website.

Duane Benson
A = sd1
V = Ad2

PCB Panelization at Screaming Circuits

Most design and manufacturing type folks wouldn’t dream of sending a 2” x 3” pcb out for high-volume manufacturing as a single board. It would generally be replicated up to a panel (also called an array by some) size that would fit the volume manufacturers equipment and would yield the largest number of boards.

In the prototyping world, though, that usually doesn’t make sense. With a prototype, it often makes sense to run just few boards in case there are design errors. That’s why we usually assemble single boards and don’t require any tabs, fiducials or things of that sort.

Sometimes we do get requests to assemble panels and we generally can do that without problem – provided we have the right information at the right time.

If you want us to assemble a full panel of boards, you should still quote the individual board. For example:

• Your design has 25 different bill of material line items
• You have two panels, each with ten boards
• Each board has 45 smt placements on it.

On our website, you would quote the “Desired board quantity” as 20 boards, with 25 “Total # of manufacturer part #s” and 45 “SMT” placements.

Then, in the “Special Requirements / Comments for Assembly” box, tell us that the boards are panelized ten-per-panel and tell us if your Gerbers are panelized or single.

Family panels are another issue altogether and will be discussed in a separate posting.

Duane Benson

If There are Questions

On May 8th,1884, Harry S. Truman, 33rd President of the United States was born. Also on May 8th, 2007, we made a few changes to our order process as described here. On the "Place you Order" page - the next one after the quote - we changed a couple of key questions.

Under the header "PARTS INFORMATION" we ask you: "If we find minor problems with your kit, such as BOM mismatches, missing parts or mis-matched pads, should we..."

This is a VERY IMPORTANT question.

Sometimes we will find small parts substitutions because the specific design, it doesn't matter. Yet, it might just matter. Read this post here. We can't tell without knowing all the details. This question is your opportunity to tell us if it matters.

Sometimes a kit will be short a few parts but the customer still wants to get the boards built up as soon as possible regardless. We can't tell without knowing all the details. This question is your opportunity to tell us if it matters.

If you want us to double check you as much as we can, select the "Call to discuss..." option. If we see anything out of the ordinary, such as: BOM mismatches, parts shortages, missing parts, parts that need to be baked, pads that don't fit quire right or other similar anomalies, we will stop the build and call you. This may delay your job and will not be covered by the delivery guarantee.

If you just want to get the boards back ASAP and don't care if you are short or missing a few parts or have a mismatch or two, select the "Build as much as we can..." option. This does mean that if you think C2 is a 10uf, 16volt cap and you mark a bag of 100uf caps as C2, we will put those 100uf caps on the board, or if you need 100 and send us 85 we'll stuff the 85 and send the boards back to you as complete, or if you forget to send any of IC U3, we will build without it.

We want to build your boards fast and accurate, but even more than that, we want to build them the way that you need them. This question is your opportunity to tell us.

Duane Benson
Enquiring minds want to know. Or, so I've heard.

Moisture Sensitive Parts

Avoid moisture-caused delays.

Most of you have probably seen the "moisture Sensitive" components symbol. Most of you probably understand its meaning and significance. However, in the topsy-turvy world of prototyping, details sometimes hide when they shouldn't.

From time to time, we receive moisture sensitive components that are not sealed in moisture barrier packaging. This means that we have to treat it as though it has absorbed too much moisture - and usually it has. According to the JDEDC standard, J-STD-033B.1, there are quite a few ways for components to be at risk. If the components are at risk, according to the standard, we are supposed to bake them for 48 hours before assembly.

Naturally, if you need a 24 or 48 hour assembly and we have to bake for 48 hours, something doesn't fit. If you don't want the components baked, but want them used as-is, please tell us in the special instructions when you place your order. If you don't tell us, we will try and contact you. If we can't get ahold of you, we will do our best to determine the risk and we may stop your job to bake the components. If we do have to bake them, your turn-time guarantee starts after baking.

The best procedure is to leave the components sealed in the original moisture barrier packaging when you ship them to us. If you open the packages, please let us know your preference for baking or no-baking. Take a look at our earlier MSD post for a bit more information.

Duane Benson
Baking should be for cookies, pies and cakes.

Production???

So, if you read this blog or have placed an order since Tuesday, you know that we have made some updates to our order process. If you don't read this blog or haven't placed an order since then, read the post just before this one to find out what I'm talking about.

I'll wait.

Done?

Okay, in the "Place your order" page, we now ask you if this is a prototype or a production build. We are prototype specialists, so why would we ask this question? Well, yes, we are prototype specialists, but it turns out that building small quantities of prototypes really fast, in some cases, ends up being just what the doctor ordered for small production runs. We don't actually do anything different than with our prototype builds, but a sizable number of you have told us that you use us both for prototypes and for small volume production builds.

That's where this question comes in. By asking that question, we end up better understanding what you need us to do. Eventually, we will likely change the process a bit for production orders. Whatever we do though, it will still be easy, convenient and fast for you.

Duane Benson
Is "protoduction" a word?

Web Site Update Notice

We will be making some updates to our website quote and order pages on Monday, the 7th, at the end of the day. [It went live Tuesday, the 8th]

We are expecting no more than 30 - 60 seconds site down time. Unless you are right in the middle of an order, you probably won't notice.

For the most part, we are just cleaning things up a bit, making the layout easier to read and putting more of the important tidbits of data in front of you.

1. We've changed the tab-order for the quote page and improved the formating so that a quote will print better.
2. We will now display your order number as soon as you select "Place your order." You can use this order number when calling us with questions. Previously, you didn't get to see your order number until you had completed the entire order process.
3. We have changed the parts information questions. Now we ask if you want us to stop work and call you if anything is out of the ordinary with your build or go ahead and build as much as we can with what we have.
4. We ask you if this is a prototype or a production order. The process doesn't really change, but it helps us to understand your needs a bit better.
5. We ask for an emergency, after hours contact name and phone number so we can get those questions asked and answered even after hours and reduce delays.
6. On your "My Accounts" page, we now list past orders and saved quotes with the most recent at the top of the list.

Unless something comes up, we will put these in place Monday at about 5:00pm Pacific time. Our site may be off line for a short period of time when the changes are turned live.

Duane Benson

Parts Substitution

Take a look at the two parts in these pictures and see if you can guess what the difference is. It's the same two parts in both photos, just a top and a bottom view. Click on the images for a close-up view.

I'll give you some hints. They are both Schottky diodes. The photos aren't quite clear enough to read the part numbers so I'll give you that one. They're both from International Rectifier. You can kind of see the "IR" on one of them in the photo, but not the other. The foot print looks pretty much identical - both SMA packages.

Enough with the suspense. I'll answer the question from three different perspectives.

One is an IR 10MQ100N, 100V, 2.1A with a Vf of 0.68volts. The other is an IR15MQ040N, 40V, 3A with Vf of 0.43V. From the perspective of Screaming Circuits process technicians, these are two completely different parts. If the BOM called for one and we saw the other, we would have to stop the build and try and call you. Doing so might very well delay your job, but we would have to do it.

So, is there really a difference? Are we right or wrong to stop the build?

Design A is a triple voltage (12, 5 & 3) DC to DC converter. It takes 15 to 30 volts input and converts it to the three outputs at a combined maximum current of 1.0 Amps. The diode, in this case, is used for reverse voltage protection at the input. Either diode will work fine in this application. The 40V, 3A would provide a little more current head room and cause less of a voltage drop for a bit more margin on the low-voltage end. The other one would give more voltage overage head room. For the purposes of a prototype, though, they are effectively equal in this application.

Design B is a free-wheeling diode application in an H-bridge motor driver. The maximum free wheeling current is expected to be under an amp at approximately 48 volts. Elsewhere, the circuit is spike protected with 72 Volt TVS diodes. In this case, the 100V part would fit the requirements and would give adequate headroom. The 40V part might very well smoke at first turn on.

For designer A, the parts are completely interchangeable in a prototype. For designer B, putting the wrong one in could smoke the part, and potentially also damage some mosfets and an expensive mosfet driver chip. We can't tell which is the case, so we have to assume the worst case and stop the build. It's the same with close but not exact value caps and resistors. We have to assume the worst and stop the build.

If you do need to sub, change the BOM before you zip it up and send it to us or at least tell us in the special instructions section of the online order form. If you make the substitution after you've placed the order and sent us the files, give our customer service folks a phone call (866)784-5887. We don't want to delay your project, but we REALLY don't want to smoke it.

Duane Benson
Where there's smoke, there's bile