Click to expand.Hello,but routing of the signals might be difficult using 3 signal layersinstead of 4. It may be possible to use one signal layer for verticaltraces, one for horizontal traces and one for traces with 45 degreesdirection. But using two layers for vertical traces and one forhorizontal traces may result in crowded horizontal traces and a lot offree space between vertical traces. It depends on the shape of the boardand the placement of the parts what configuration will be useful.Bye.
Click to expand.To say that 'return current' is a myth, flies in the face ofconsiderable research, modeling, and empirical evidence. Not to mentionthe simple fact that circuits must be complete in order for any currentto flow.So perhaps you could elaborate on exactly what you mean?As I understand, and this seems to be backed up by many papers, and evena few visual demonstrations, is that return current does indeed flowunder a trace, in the nearest plane. If that signal hops to anotherlayer which is closer to another plane, then the return current mustalso hop. It may do so through the distributed capacitance, throughstitching vias (which can only be applied between planes which areequipotential at DC) or through bypass caps.For signals switching between different DC voltage planes, then it isusually a combination of distributed capacitance and nearby bypass capsthat accommodate the return current traversal between the planes,depending on frequency, the inductance of the bypass cap connections,and the spacing of the planes.Every traversal represents an impedance discontinuity. An analogoussituation would be to take a coax cable, and cut the shield all the wayaround, leaving a gap of about 1 mm.You certainly wouldn't propose that such an interrupted cable functionsnormally?It could be made to behave similarly to a PCB trace running over a slotor switching reference planes by taking a piece of hookup wire with aloop area large relative to the Z0 of the cable at a particularfrequency, and soldering the two pieces of shield back together with thewire loop.
Click to expand.Sorry but that is total crap. Its like saying a gas station putsgasoline in your car this week and next week its diesel. The company I'm referring to (Eurocircuits) has the stackupsspecified on their website and they make the boards themselves inseveral factories across Europe. They deliver what they promise.Your assumptions maybe true for a shabby PCB broker who orders fromthis week's favorite Chinese.
Rearrange the layer Stackup in Allegro Just make sure that via definitions allows what you want to do. Thru-hole vias are of course OK, but buried or blind vias can mess things up a lot.
I wouldn't order PCBs from such acompany to begin with. 1 SIG1 & COMP8 mil FR42 GND10 mil prepreg3 SIG28 mil FR44 VCC10??
Mil prepreg5 GND8 mil FR46 SIG310 mil prepreg7 GND8 mil FR48 SIG4 & Misc Bypassthat way smaller trace widths on the outside layers can givecontrolled Zo,being 3 layers, GND plane itself has lower impedanceVcc & GND are close together to gain advantage of 'free' capacitanceIf you need it, even SIG2 and SIG3 layers can yield fairly wellcontrolled ZoOk, Ok, Can't addd the extra layer?Can you go to 32 mil total? Click to expand.Of course not. But you've got the dimensions wrong: the gap might be 0.25mm(i.e., 10 mil, or even less), not 1mm.
This lets out a lot less fluxalready (both E and M).Be interesting to see just how much crap gets lost over such adiscontinuity; like a scope probe with ground clip, it's not going to bepretty by any stretch, but it's also not going to be as bad as DC intuitionsuggests.This would only be true of a board with a single, slotted ground plane,which is silly by any measure. The correct analogy would be if you tookthat injured coax cable and wrapped it with copper foil tape, so that theshield is supported all around by a secondary ground plane. The currentflows as displacement current in the outer jacket; high frequencies willhardly know the difference.Very high frequencies will know the difference, on the order of slot width= 1/20th wavelength. Low frequencies will know as well, but that's easy,because at low frequencies you can simply hook a wire to either side of thegap and handle the LF current that way.John uses many planes, and only two planes are required for operation - aslot in one pour, or a gap between different pours, supported beneath bypours bridging said gap.Tim.
When I first started building projects in and around my house, I learned very quickly to consult the experts when it came time to select my materials. For instance, the instructions for a tool shed that I built specified a certain roofing material that was pretty expensive. After asking at my local home improvement store I found out that for our climate, the ultra-robust roofing material listed wasn’t needed and was, therefore, more expensive than the standard materials.When you are creating the PCB layer stackup on your board design you will probably run into a similar scenario. You may not know the best PCB materials to use or how to effectively construct the stackup. It will be in your best interest to understand what you need before you commit to anything. Optimizing your design means sorting through hordes of variables to consider and choose from. I can’t tell you what you should do, but let’s take a look at some of the ways that you can find out what you need to know about PCB layer stackups before you proceed with your design.
Work with Your Manufacturer for the Best PCB Layer StackupOne of the best sources of information that you can leverage when creating a PCB layer stackup is that of your board manufacturer. They will be able to work with you to figure out what you are trying to do with your board design, and then tell you the specifics of what you will need to successfully fabricate it.When first setting up your board, consider the many different parameters and make sure to give your manufacturer as much information as possible about the board you are designing. For instance, you will want to tell them the following:.Purpose of the board: Knowing what the board is supposed to do will help them when they make their evaluation of what materials and stackup should be used. On the same hand, knowing in what environments the board will live will alter what materials will be best suited.
High-moisture environments could alter a design entirely.Board technology: They will want to know what kind of parts are being used, and whether or not the board will have high speed circuits on it. High speed designs may require different materials and/or unique board layer stackups signal performance.Board size: The manufacturer will want to know what size the board is in order to determine what panel size will be needed for manufacturing.
Not only is it more cost effective to maximize the number of individual boards that can be put into a panel, but it will affect how the board layer stackup is created and what materials will be used.Cut-outs, holes, and special features: Like the board size, this information could make a difference in what the manufacturer decides is the best way to go in setting up your board for fabrication and assembly. Drill hole files and information for plated through-hole (PTH) or non-plated through-hole (NPTH) will also be helpful for your manufacturer.There is a lot more information that your manufacturer will need, and they will present you with a complete set of questions on your design so that they are as prepared as possible.
The important thing is to work with them early so that you can start the design in the right direction.The last thing you want to do is to have to do a major redesign because the manufacturer can’t make a board layer stackup the way you devised it. As it has been said, “Design your board according to the way that the manufacturer has specified it be done instead of how you think it should be done. This is what these people do every single day for a living, and they are good at it!”Your manufacturer will be a great resource for complex PCB layer stackup informationPCB Design Resources and Help are Out There—Use ThemAs I mentioned, your PCB manufacturer will be the first best resource to go to for information on how to create your board layer stackup. There are, however, many other resources that you should look into as well for a helping hand. If you are working for a company that has been designing boards, find out what they have been doing for similar designs. Also, seek out help for those you work with, and don’t be afraid to consult blogs and white papers for information as well.
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That is what they were written for.Another good resource to use is online impedance calculators and layer stackup generators. Many printed circuit board fabricators have these available for you to use, and they can be a big help. You can also find additional information on layer stackups from organizations such as IPC.The Cross Section Editor in OrCAD PCB Designer is a great tool for creating stackupsPCB Design Tools that Can Help You Work with PCB Layer StackupsOnce you’ve decided on what kind of board you are designing, and you’ve consulted with your manufacturer so that you are synchronized with them, it is time to start to design your stackup. Here is where having the best PCB design tools that you can get at your disposal will be a huge help. With advanced PCB design tools you can specify the complete layer stackup of your PCB design including the materials and widths of the conductor and dielectric layers. With this information built into the system you will have complete fabrication data that can be used for calculations, simulations, and eventually output documents and drawings for manufacturing.The that we use is OrCAD PCB Designer, and with its cross section editor it can create PCB layer stackups in full detail.
Is a powerful set of design tools giving you the ability to capture and simulate your design in a schematic followed by creating the physical design in layout. Furthermore, if you are using the format, you can have your stackup imported from your vendors.If you’re looking to learn more about how Cadence has the solution for you,. About the AuthorCadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.
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