What precision do I need to route a DSP? - Page 1
Forum section: electronics / general

author: Ferrita
author_rank: Contributor
timestamp: August 20, 2025, 04:51:51 am
content: I need to add a DSP to my project. The problem is that these components have a high pin density and are very close together.My current precision is 0.1 mm.Texas Instruments DSPs have a pad spacing of 0.2 mm. If I add 0.1 mm of margin to each pad, it means both pads are glued together.Analog Devices DSPs have a bit more margin; they have variable pin widths (from 0.18 to 0.3 mm), but I depend on finding a footprint with pads that aren't wide. Since I don't know the exact pin width, I'm hesitant to make the footprint myself and depend on finding narrower footprints. Even so, the largest margin I've achieved is 0.046 mm (ADAU1451WBCPZ-RL), and with only one DSP, so I can't choose the DSP because, according to my rules, I can only use one.How can I use DSPs, ADCs, etc., with pins so close together? What precision should I use? Is increasing precision on a PCB expensive? Do common manufacturers work with precisions less than 0.1 mm?---------------Image with pads margins DSP -->https://ibb.co/s9GmKHrMIt's a safety margin applied to the tracks and pads. It's called clearance, and it can't be less than the precision you're going to use (0.1 mm).Margin explanation:https://electronics.stackexchange.com/questions/572316/what-are-the-boundaries-around-pads-in-kicad-pcbnew-and-what-are-their-functionsIt's a safety margin applied at the network level, just like the track thickness:*** Image -->https://ibb.co/Kz8jkCdtIn the ADAU datasheet, the image of the dimensions is the same for all components. The pin thickness isn't exact; it's a value within a range of 0.17-0.27 mm or 0.18-0.3 mm. I don't know the actual pin width; I only know the pad widths in the footprint I downloaded.*** Image -->https://ibb.co/7t1TgfbDI can't use any Texas Instruments because it's not possible with my clearance zone; there's no safety margin.I'm going to ask the company to do the soldering.Declaring a clearance zone and setting the value to 0.1 mm (equal to the precision) was the advice of the IA, but from what I understand, it's good and necessary to consider the manufacturer's margin of error for greater safety.Is my clearance zone incorrect?

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 20, 2025, 01:44:58 pm
content: The ADAU1452 has 0.5mm pitch. Pad width would be 0.25-0.3mm. By today's standards this is a trivial package to design for, any PCB fab should be capable of 8mil trace/space without issue.

author: Ferrita
author_rank: Contributor
timestamp: August 21, 2025, 12:34:36 pm
content: Hi mtwieg! Thanks for participating.Accustomed to routing components like the ESP, the DSP is my first small challenge, and I have no experience. Looking at the image data, I thought something in the configuration wasn't right or correct for this situation. The margins are very small, and others have no margin at all.My clearance is 0.1 mm (in the image: the outline is larger than the pad and the same color), and I think it's the correct configuration for a precision of 0.1 mm.Comparison Image -->https://ibb.co/s9GmKHrMDo you think I can build a PCB with such small margins? And if it's not a safe margin, what should I do to resolve the situation?

author: Berni
author_rank: Super Contributor
timestamp: August 21, 2025, 12:46:10 pm
content: All of the big well known PCB manufacturers can do very tiny stuff. The question is just how much they charge to do it.I never heard of them specifying precision tho. They all specify minimum track width and minimum track spacing. Something like 0.2mm track width and space is pretty standard and JLC PCB will make such a board for 2$. This covers all of your usual TQFPs QFNs..etc down to 0.5mm pitch or even 0.4mm pitch.When you get to things like 0.4mm pitch BGA chips in dense layouts then the PCB requirements get much much harder, you need tiny traces, tiny via holes (laser drilled vias, or via in pad), many layers...etc. At that point you start having to pay 1000$ for just 5 prototype boards.

author: shabaz
author_rank: Frequent Contributor
timestamp: August 21, 2025, 02:09:15 pm
content: Quote from: Ferrita on August 21, 2025, 12:34:36 pmAll of the parts listed in the image are easily for any PCB manufacturer to do, none of them have particularly tiny packages.You seem to be referring to solder mask between pads. It's not mandatory to have solder mask between pads, although it can help in some cases. You can refer to the datasheets for recommended pad layout, including solder mask detail. Is this your first PCB? in which case, if you're unsure, you could simply make a small PCB with all your proposed footprints on it, and submit it to a low-cost PCB service, and see what you get back, and use it to practice, to learn what you're comfortable with soldering too.

author: Ferrita
author_rank: Contributor
timestamp: August 21, 2025, 11:53:54 pm
content: Hi Shabaz! Thanks.Ref Image with margins -->https://ibb.co/s9GmKHrMI'm not referring to the solder mask. It's a safety margin applied to the tracks and pads. It's called clearance, and it can't be less than the precision you're going to use (0.1 mm).Margin explanation:https://electronics.stackexchange.com/questions/572316/what-are-the-boundaries-around-pads-in-kicad-pcbnew-and-what-are-their-functionsIt's a safety margin applied at the network level, just like the track thickness:*** Image -->https://ibb.co/Kz8jkCdtIn the ADAU datasheet, the image of the dimensions is the same for all components. The pin thickness isn't exact; it's a value within a range of 0.17-0.27 mm or 0.18-0.3 mm. I don't know the actual pin width; I only know the pad widths in the footprint I downloaded.*** Image -->https://ibb.co/7t1TgfbDI can't use any Texas Instruments because it's not possible with my clearance zone; there's no safety margin.This is my first PCB, so I'm not going to solder the parts; I'm going to ask the company to do the soldering.Declaring a clearance zone and setting the value to 0.1 mm (equal to the precision) was the advice of the IA, but from what I understand, it's good and necessary to consider the manufacturer's margin of error for greater safety.Is my clearance zone incorrect?You say "the parts look easy to manufacture," but my rules don't allow it (my clearance for tracks and pads). What am I doing wrong?

author: shabaz
author_rank: Frequent Contributor
timestamp: August 22, 2025, 01:17:39 am
content: QuoteI don't know if you've changed any of your rules. See attached example settings, I usually have no problem with these with typical PCB manufacturers, with the settings shown.I don't know what Texas Instruments library you're referring to; if it doesn't come as standard with KiCad, then there could be an issue with that perhaps. I create my own symbols and footprints usually, or sometimes use the ones supplied with KiCad, either as-is, or copied-and-modified.

author: Ferrita
author_rank: Contributor
timestamp: August 22, 2025, 08:54:58 pm
content: Thanks, Shabaz. The setting I'm referring to is the 'net classes' clearance:*** Image clearance in net classes -->https://ibb.co/1JzMxqSBThat clearance is the margin seen on the pads.*** Image clearance pads -->https://ibb.co/M0kcQ0NIf a pad measures 0.3x0.6, with the clearance it will measure 0.5x0.8 (add 0.1 on each side).That clearance causes the pads to touch or be too close together. My clearance for all nets is 0.1mm; this is my problem, but I've never seen a clearance value lower than 0.1mm. I can change this value to 0.05mm, for example, and the pads already have more margin, but I don't know if it's a valid solution.The pads shouldn't touch or be too close together, but that's my situation with the clearance at 0.1mm.

author: shabaz
author_rank: Frequent Contributor
timestamp: August 22, 2025, 09:20:38 pm
content: I don't fully understand, but if you're saying that you're getting a design error because 0.1 plus 0.1 equals precisely 0.2 and that's too high, then why not change your 0.1 value to (say) 0.099? The PCB won't have that level of precision, whereas computer software can. Then you won't see the issue, both in software, and in real life on the PCB since you can't resolve 0.002 mm.EDIT: Or, even easier, simply reduce your pad width by 0.001 mm or so, if you don't plan on changing the rules.

author: aeg
author_rank: Regular Contributor
timestamp: August 22, 2025, 10:20:40 pm
content: There's no such thing as margin or precision. "Margen" in your native language is correctly translated as "clearance", also known informally as spacing. Set track width and clearance to the trace/space capability of your PCB house. Distance between copper on separate nets must be equal or greater to clearance. That's all. All of the "cannot be manufactured" examples in your comparison images can be manufactured.