Horizontal integration. Vertical integration. Multidimensional integration.
Episode 1: horizontal
Strange enumeration, isn’t it? And – believe it or not – it has to do with PCB development, which makes it even stranger, I guess.
Let me explain: I am talking about the integration between different stages of the PCB design flow (horizontal), between different design engineering domains involved in this flow (vertical), between engineering and logistics (third dimension), as well as between development and field operation (fourth dimension = time).
In order to achieve the highest productivity and quality, intelligent information must flow on each of these axis, in an automated and bidirectional manner.
Let’s use some examples for better understanding. The PCB flow is made of several stages: concept (schematics), verification (simulation), implementation (layout), fabrication (bare board), assembly (pick & place), testing (ICT, flying probe). Schematics must be available for simulation without human intervention, thus without room for human error (we must not re-create the schematics in the simulator) and with as little user effort as possible. Simulation will yield a set of rules (constraints) which will drive implementation (forward annotation), but might also affect schematics (back annotation, e.g. I need to use a different part or change the termination strategy). These results must also be transferred automatically to the implementation stage, so that we do not risk the user types the wrong value into a maximum length box.
When we do the layout, we should account for the technological limitations of the fabrication process (e.g. minimum trace width, minimum clearance), so that we do not finish it only to find out all our traces are too narrow. We should also run design-for-fabrication checks, so that we correct those pesky acid traps right away and not wait one week for the fabricator to tell us where they are.
By the way: how will the fabricator let us know where the problems are? Preferably with an intelligent transfer of information, such as a violations report attached to our layout. If they only sent us notes on a printed drawing, chances are we might oversee some of those issue. So you see why intelligent information must flow both up and down the process.
But, hey, is this fabricator able to produce the layer stackup which I need? No?!! Damn, then I have to start all over again, because my trace impedance will change and all my routing is now worthless. This example underlines the need for what is called left-shifting: all process stages must propagate as much information as possible to their “left side”, which means to stages which are earlier in the process. If, while performing a certain stage, we are aware of the constraints imposed by later stages, we are able to reduce the number of iterations. Stackup is only one example. Think about flying-probe testing: maybe our probe cannot reach a certain testpoint because the component package is too tall. If we have this information before starting the layout, then we could choose a different package or adjust the placement of that component so that it does not get in the way.
What if I do not go back to change the stackup and just find another fabricator? Well, probably this fabricator will cost more and this hints to what I mean by the third dimension – the integration between PCB design and logistics: cost, delivery time. The example with the component package being too tall hints to the meaning of the vertical integration: PCB design and mechanical design. More on this in the next episodes…