# Designing a PCB layout without having a schematic diagram (or netlist)?

Could you please let me know if it's possible to design a PCB layout without a schematic diagram?

I outsourced the development and manufacturing of the ARM board which has 512MB DDR3 RAM and 4GB eMMC. The outsourcing company promised to make it in 45 days, but they didn't give me the product even it's already more than 100 days from beginning of the project. When they said they were manufacturing its PCB last month, I asked them to send its schematic diagram. But the answer was that they didn't finalise the schematic diagram and need 2~3 days to make it. As far as I know, you can't make PCB without importing a netlist from a schematic diagram file, especially when you have two DDR3 RAMs. It has been 1 month from the time and still I don't have the product. I need to decide how to react and would like to know if the company lied.

I spent about $6,000 for the outsourcing and now I have no idea what to do. • I think you're looking for SE:Law May 25 '16 at 6:10 • @Daniel at least I need to know if it's possible and make sense. – SD11 May 25 '16 at 6:14 • I would say that your question is legit - it's an electrical engineering question. Even though it could be more specific. Hope everything works out for you. Based on my knowledge of making PCBs it would be a total mess to make a board without a schematic. It makes no sense. May 25 '16 at 8:05 • If you have not yet paid then don't pay. If you have already paid then it's probablly time to talk to a lawyer. May 25 '16 at 9:16 • If they said they are having boards made, then you can ask for the gerber files. They'll probably say they're making boards without the gerber files though.. May 25 '16 at 9:29 ## 6 Answers It is technically possible to design a PCB layout without first completing a schematic, but extremely unlikely. It just makes it unnecessarily complicated. I think whoever you hired is not being fully honest with you. I think a likely alternate explanation is that the company you hired turned around and outsourced the project to yet another company! But they may want you to believe they are doing the work in house, so they're keeping you in the dark and coming up with weird excuses. It's also possible that they are doing the work in house, but underestimated the skill level necessary to complete a board of that complexity (it turns out that high-speed signals are hard to design for). So they're stringing you along until they figure it out. Either way, your prospects don't look good. I would think very seriously about trying to get your money back and go with a company that can keep their promises. • It's possible, but it would be a rookie mistake. Do not do business with this company. They're either lying or incompetent. – Mast May 25 '16 at 9:26 Is very possible that the pcb files you have do not correspond to the circuit you want. it "smells" like they just took a similar board and just gave you the finish board. Not supplying the schematic is a bad sign. my humble oppinion is they are playing with you. Be carefull, never pay for dev in advance, or bad stuff can happen to you. • But usually all companies will ask for an advance payment. I have not worked with any pcb design firms but have outsourced a few logo design and other similar jobs. In all cases, half payment has being asked as an advance and other half during delivery. Wasting half payment and that much time is also a pretty bad situation. May 25 '16 at 11:54 It's possible to lay out a PCB without a schematic but the chances of error are extremely high. I would consider anyone who would do it for a non-trivial design (and this design is far from trivial) to be incompetant. It is possible that there is a schematic but it's not in a state where they consider it fit for release. For example component values may be missing or it may just be very messy (on complex board you inevitablly end up modifying the schematic to swap pins arround while you are doing the layout, so it can make sense to leave tidying up until after layout). It's also very much possible that they lied about having the boards made. • I once made a PIC32 ARM board without a schematic (don't ask why). It was hell. It also didn't work at the end. May 25 '16 at 12:40 • A board for a microcontroller is far simplier than a board for a processor with external memory. Doing the former without schematic capture is stupid but doable, doing the latter without schematic capture is getting into the realm of the ridiculous. May 25 '16 at 12:52 • Totally agree. I mean, you'd have to route perhaps (160*2 for the ram, + 50 for mmc, + ~250 for a small bga processor...) = 650 traces... without airwire guides? That is not doable. I wouldn't even do that without autorouter, but that's just opinion. Oh, and, this board probably requires impedance controlled lines on some high-freq pairs, so you would have to do all that manually. May 25 '16 at 12:56 As an addition to the absolute correctness in Dan's answer the only possibility I see for there to be the smallest hint of truth is them using a set of pre-made blocks from a library as smart companies would and them having to re-do some stuff to not expose the entire library. Apart from that the total run time on this is about a factor 5 over what I would need based on the limited details, so I would abandon these people permanently whether or not they lied. But then, as @Daniel says in a comment: My fee is nowhere near as low as$6000. It might be just about enough as a down-payment given a proper contract with deliverables and payment obligations was made along with it.

I just wanted to add this (and it didn't fit in a comment) for balance and clarity that not always not wanting to give the schematic right away when the boards were already ordered means something untoward is happening.

I routinely design complex PCB layouts before I create the schematic. However, this is not a practice that I recommend for anyone else.

For me, it's easy. I have an extremely detailed picture in my head of what I want and I simply do the layout. When I'm done the layout, I extract the netlist from the layout and use my CAD package's back-annotation process to create the schematic. I can then check the schematic for errors and omissions.

I can do this because I started laying out complex PC boards long before there was inexpensive CAD systems available. I'm talking about the Bishop Graphics Puppets era here - and even the time period before Puppets were available.

Not having a computer to manage your netlist means that you need to keep your schematic in your head. Do this for a long enough period and it becomes second nature.

This process is good (for me) for up to several hundred nets. Once the number of nets get into the thousands, I do things the way everyone else does: create the schematic, then use the netlist to create the PCB layout.

Where I'm going with this is that it IS possible that your subcontractor has done things this way. Unlikely, but possible.

Depending on the software, one could ratsnest/manually write a netlist, then layout, following a schematic that is not in electronic form or that only exists as a description ("look at the datasheet and connect that group of pins to that according to the numbers"). Alternatively, one could generate the netlist directly with some non-visual tool (eg a perl script).

• I was not RECOMMENDING that practice, and the question was partially about how there could be a layout but no schematic. May 30 '16 at 14:52