Hi,

Consider a circuit with a hex inverter. In the circuit diagram the 6 units in one package are functionally interchangeable. In the PCB layout there are 6! permutations and as many different rats nests to untangle. Some of these will be closer to optimal than others from a PCB layout point of view.
Then suppose there's another gate type in a package of 4 in the same circuit. Now there's a bunch more (6!*4! ?) 'graphs' to base the layout on.

Is there a method or strategy beyond eye-balling it to narrow down the best candidates?

 

Hi,

Consider a circuit with a hex inverter. In the circuit diagram the 6 units in one package are functionally interchangeable. In the PCB layout there are 6! permutations and as many different rats nests to untangle. Some of these will be closer to optimal than others from a PCB layout point of view.
Then suppose there's another gate type in a package of 4 in the same circuit. Now there's a bunch more (6!*4! ?) 'graphs' to base the layout on.

Is there a method or strategy beyond eye-balling it to narrow down the best candidates?

Place them on the PCB the best you can knowing you will later have to "swap pins" and/or devices.
You might try using "groups" if the software supports them.

 

Hi,

Consider a circuit with a hex inverter. In the circuit diagram the 6 units in one package are functionally interchangeable. In the PCB layout there are 6! permutations and as many different rats nests to untangle. Some of these will be closer to optimal than others from a PCB layout point of view.
Then suppose there's another gate type in a package of 4 in the same circuit. Now there's a bunch more (6!*4! ?) 'graphs' to base the layout on.

Is there a method or strategy beyond eye-balling it to narrow down the best candidates?

Not that I have ever heard of, but I'm NOT a layout specialist.

 

Hi,

Consider a circuit with a hex inverter. In the circuit diagram the 6 units in one package are functionally interchangeable. In the PCB layout there are 6! permutations and as many different rats nests to untangle. Some of these will be closer to optimal than others from a PCB layout point of view.
Then suppose there's another gate type in a package of 4 in the same circuit. Now there's a bunch more (6!*4! ?) 'graphs' to base the layout on.

Is there a method or strategy beyond eye-balling it to narrow down the best candidates?

I don't know of any formal way, but you can usually to pretty good by using an incremental approach. There's often some low hanging fruit given how they need to interact with connected parts/nets that they are attached to. Put those in first. Then add another gate and see if it fits nicely into one of the unassigned spots and, if not, see if there are swaps that can be made that improve things. Continue until you have everything in.

 

most my designs are mixed circuits and moderately complex (5-25 pages of schematics, rarely more). when doing layout i select portion of a circuit in schematics editor, this also highlights selected components in the PCB editor, making it easy to drag to a side and treat as cluster. each cluster is arranged and routed independently. if there is a tangle, it is treated locally - within own cluster. important things are routed first. then clusters are placed next to each other and interconnects are routed as well. like with courier problem, there is no need to evaluate every possible iteration, one glance is enough to tell difference between atrocious and reasonable. multi-layer boards exist for a reason. so far most of my projects are 2 or 4 layers, sometimes 6 or 8 layers... most PCB houses can easily do 32 layers.

 

Assign gates connected to the same signals or nearby components to physically convenient package units. This reduces routing length and crossings. Tools like KiCad can help automate placement and routing. However, automatic gate swapping depends on the tool and its support for equivalent units. You can find this write up helpful. How to Design the PCB Board. It discusses about changing gates or parts to improve routing. This Kicad thread may also help. Automatic Optimized Parts placement on PCB.