ciruct board assembly time!

You can have the most beautifully crafted and electrically perfect circuit board ever produced by man, but if it has the wrong parts installed it won't be worth a penny to you!  Obvisouly, it's your circuit board assembly provider's job to nail this opertion perfectly for you.  So what can you do as a customer to insure your provider can do the best job possibe?

To be clear, it is the customer's main job to provide the most accurate information for the entire circuit board fabriation and assembly process.  One of the area's customer's fail the most is in providing a clean Bill of Material or BOM.  Like previously stated, if the assembly is wrong the printed circuit board will never function as intended.  A clean and accurate BOM will help with not only creating the fastest and most accurate quote possible, but more importantly, the fastest and most accurate assembly.  This includes both customer supplied part kits and part aquirement services, so don't assume that if you are supplying the parts the BOM doesn't need to be on point.  Your BOM should be generated from your CAD software tool along with your other fabrication files.  Let's dig into how your BOM should look and what information is most important to include.

Typically, too much information is never a bad thing when it comes to your Bill of Material.  Most BOMs are generated with columns of information with each column supplying information and rows of line items of each unique component.  Here are the things that should be included in your BOM as a MINIMUM:

• ALL reference designators (if they are Do Not Popluate or DNP it's still best to include)
• Refrence designators utilitzing the same part number should be grouped together as as single line item.
• An MFG part number for each unique part being placed. (Certain exceptions can apply)
• Exact quantity for each part.
• A brief part discription (most critical for passive components)

If your supplied BOM is missing ANY of this informaton, you need to STOP, go back to your CAD software or vendor, and get this information added at a MINIMUM!  

The most common issue we find even when the above minimum information has been properly provided is out date or obsolete manufacturing (MFG) part numbers.  These are generally seen in older designs, but some professionals use CAD libraries that have been develped over the coarse of years, this can lead directly to the use of obsolete parts in new designs.  It's extensively seen in passive components, but many times active components can and do become obsolete, as well.  This is why supplying accurate discriptions is important for passives especially.  These discriptions should include some or all of the following data: 

•  value
•  tolerance
•  case size
•  voltage requirements
•  current requirements.

This infomation will help allow us to make quick suggestions for drop-in equivelant alternate MFG parts.  This will help in saving time and typically a lot of costs as drop-ins will be cheaper to aquire than orignal parts that are now obsolete and no longer manufactured.  

Providing a good list of approved equivalent drop-in alternates for as many parts as possible is highely recommended.  This will help save time and avoid unneccesary holds on the quote or assembly while waiting for customer approval.  Of coarse, alternates are not always a possibility.  In cases where orginal parts cannot be purchased, substituted, or have long lead times it is up to the customer on how to proceed.  

Besides a clean BOM the second most important document for a circuit assembler to have on hand is a good centroid file.  This file provides a list of X, Y coordinates for each component on the board as well as a theta orientation value.  This file is essential for a fast and accurate assembly.  Some very simple assemblies don't always require a centroid as we can manually program, but when there are dozens, hundreds, or even thousands of components in a single board assembly you start to understand the vital necessity of such a file.  

Centroid location files are generated inside your CAD software along with the rest of your data files for fabrication.  It is typically in a .CSV file type and should have the following minimum data:

• Refrence designator for each part
• X and Y coordinates for each part
• Theta value for rotation
• Top or Bottom assembly designator
• MFG part number

IMPORTANT:  Before generating location data, please verify the reference point (0,0) location is physically located at a board corner edge or some other hard point physically within the PCB layout.  A hard point can be a mounting hole or other TH.  We will need to match your reference point when we load your data into our programming software.  If you reference point is floating somewhere off in space away from the acutal PCB outline in your CAD it makes it very difficult to import that data correctly.

We are happy to accept customer supplied part kits, but we do have some strict requirements that must be met for us to even start your job.  

First and foremost, we will not start a job until ALL parts have been supplied and with proper quantity.  WE NEED MORE THAN EXACT QUANTITY!  This cannot be stated enough, but we also understand that costs need to be controlled.  We can help guide you on what you can supply close to or at exact quantity, mostly expensive IC's or other costly parts.  However, with cheap passives, the more the better.  Again, we can help give you some guidelines prior to starting a job.

Second, we require all SMT parts to be supplied in either reel, tube, or tray.  Be advised, long strips of cut tape (more than 50 quantity) will incure additional processing fees from Devil Circuit Boards as we will need to custom reel them prior to machine runs.  Long strips of hundreds of componets not properly reeled will literally be hanging out of our part feeders and laying on the floor!  That is not a good assembly practice and something we cannot allow in our assembly shop.  

We will be happy to provide part aquirement services to you where we purchase all the parts for your job (certain restrictions apply).  Many times, we actually prefer this method as it makes sure we get what we know we need to get the job done properly and on time.  

We will employ strategies that will balance what we need for a machine run of parts with what is cost effective by utliizing custom reel part purchases from Mouser and Digikey, our two main suppliers.  This does two things for us.  First, it gets all the parts on reels.  This makes it fast and easy to load into our machines for assembly.  Second, while it does add some costs for a custom reel, it's MUCH cheaper than buying full reels of expensive components.  Bottom line is our customers sit back and relax while we do all the work!

At Devil Circuit Boards, we are able to accomodate almost any type of ciruict board and, in some cases, PCB boards that other shops cannot support.  There is not much we cannot handle and we look forward to helping you on your next job!

Our machines have a hard limit of 4.5"W x 4.5"L dimension and .025" thickness.  If your supplied PCB board is smaller than that it will need to be fabricated in an array so that the overall array dimension is 4.5" square minimum and .031" thick.  If that is not possible, then we will need to charge an NRE fee to fabricate a custom PCB carrier pallet for your individual board to process through our machine so it meets our minimum requirements for both overall size and thickness.

On the larger side of assembly, we can handle a total overall board size of 20"W x 25"L total outside dimension and up to .250" thick.  Our machines are specially modified to handle these larger boards and also give us the ability to move heavy boards that some other shops are unable to process.