PCB Assembly Manufacturing Documentation with Draftsman

August 20, 2018 Peter Smith

 

In my numerous years in the electronics industry, we have come a long way. From using tape on mylars for PCB layouts to advanced CAD systems, the industry has moved what can only be described as light years ahead over the last 30 years or so.

 

Gone are the days (thankfully) of a hand drawn schematic which is then translated by someone into physical parts that are connected by hand (even in early layout programs this was true). Netlist? What was one of those in a schematic?

 

CAD tools have come along way since then, and using an advanced tool such as Altium Designer can be a significant time saver in many tasks that are rarely (if ever) provided as automation tools in other CAD packages.

 

But I digress.

 

This is the first of a series of posts where I show how I tell the story of a PCB assembly services to my contract manufacturers.

 

So; you have completed the design of your PCB (or perhaps multiple printed circuit board projects), you are happy with the layout and you have generated the files necessary to get your latest work of art actually manufactured; but have you?

 

I have seen a lot of data packs for manufacturing, from indifferent to great to, well, awful to be honest. With the advent of really fine pitch components in surface mount packages amongst other advances, the rules of manufacturing have changed as the older methods simply are not suitable for newer parts and the manufacturing pack needs to provide arguably more guidance than was sufficient in the past.

 

What type of solder do you wish them to use? What are the reflow profile limits? These are two (of many) very important issues to make sure that the soldering process yields high quality joints. Solder joints are not the only thing to consider, though. As this series of posts will show, it is possible to convey very detailed information in a way that is clear and concise with no room for interpretation.

 

When you send out your design, you know what you want to have made, but the contract electronics manufacturer does not. They do not understand the design intent, where it will be used (which implies some steps that are not part of the usual CAD tool outputs) or how to test it unless you actually provide that information.

 

To bridge this gap, PJS Electronics Ltd. provides a complete manufacturing pack with their designs. This provides the CEM with a set of documents that show everything necessary to build the design. That pack is also provided to the client so they may use their own preferred assembler.

 

There are different types of packs depending on just what is being manufactured, so I will confine myself to the simplest for this post; the PCB assembly manufacturing pack encapsulated in the rectangle. This view is the assembly hierarchy and not how the outputs are actually generated.


The hierarchy shown is a typical setup for a PCB Assembly manufacturing pack and using the tools in Altium Designer (from 16.1 onward), it is a breeze to actually make a pack that will reduce or eliminate uncertainty for your manufacturer of choice. Is it completely automated? No; every company and every design is different and there is some up front work to do which will be covered in the second article in this series.

 

Note that the pack shown is for a single assembly and could easily be a child or parent object to other higher or lower assemblies, making it ideally suited for companies with PDM (Product Data Management) / LCM (Life Cycle Management) systems.

 

Let’s take a quick look at what is here:

 

The master assembly print. Not everything the manufacturer needs to know is in the electronic outputs (pick and place, BoM); there may well be special instructions, a test procedure to be used and other information. This is often missing from many packs, but it is not difficult to generate as we will see in a future post. This is the master drawing for assembly; everything else is subordinate. In the industries I have worked in, we call this a single source of truth.

 

The schematic and BoM are standard outputs which generally already exist and we will leave these for now (but I will take a look at how they can better support both internal teams and external manufacturing in a later post).

 

The electronic PCB design data; there are nuances here that, once more, I will post about later.

 

The PCB fabrication master; this is, like the assembly master, usually not generated or sent, but all the information for a PCB fabricator to successfully make the bare circuit boards is not contained within the electronic data such as gerbers and ODB++ files. A much closer look at this will be the subject of another post.

 

A typical fabrication master front sheet from PJS Electronics Limited; there are 3 sheets in all. The Altium MiniPC example project was used to generate this document using the PJS Electronics template.

 

Test information. It is unfortunately common that the tests to confirm a PCB assembly is working after being assembled is either incomplete or missing.

 

There are major advantages to using this approach.

 

With complete information on the printed circuit board assembly, the contract manufacturer can generate a precise quote as they can properly estimate everything required; that means no surprises when a test is suddenly sent to the contract manufacturer who, apart from charging you for the test to be done, may need to put your assembly process on hold until operator time is available. Many contract manufacturers book their lines weeks and months ahead and organize their manpower and equipment accordingly. An incomplete pack can lead to a great deal of grief. Documentation and a single source of truth are key to a quality printed circuit board assembly process.

 

The PCB fabricator (often a separate company from the assembler) can generate an accurate quote as all the information they need is written down for them (my company template has 26 pre-defined comments for the PCB fabrication print).

 

Your data management team will adore you.

 

There is even a standard for these documents; IPC-D-325. By following this standard everyone understands what information is being conveyed.

 

I implemented this scheme at a company I worked for and a contract electronics assembler told me it was simply the best manufacturing pack they had ever seen. Wouldn’t you like to be able to show that email to your boss come evaluation time?

 

The bottom line: A complete fabrication pack can save time, money and schedule when done properly and there will be fewer questions and answers (although there should be some questions on a new assembly – no questions from the assembler and fabricator is a very bad sign).

 

Using Altium Designer can greatly simplify the generation of the extra drawings. There is a certain amount of time to be spent getting the templates right but that is soon amortized by the speed and ease of generating these files later in the process.

 

 

 

 

About the Author

Peter Smith

Peter Smith has over 40 years of experience providing innovative electronics and embedded design solutions including testing, fixing and design of hardware, firmware and software across widely varying systems.Highspeed / RF / EMI guru, expert in highspeed, mixed signal, analog and dense layouts. Teacher, professionally for some years, and Chartered Engineer via the UK Technology Council. 12 years Royal Navy (avionics). Co-author of the high speed signalling supplement for the InfiniBand R1.2 specification.

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