Do PCB manufacturers normalise hole sizes? - Page 1
Forum section: electronics / general

author: HwAoRrDk
author_rank: Super Contributor
timestamp: March 21, 2016, 02:57:57 pm
content: I have a board I've designed, and I feel it's nearly ready for me to get a small batch made. I'm aiming at using one of the cheap Chinese manufacturers (e.g. Seeed, Elecrow, PCBWay, et al). This will be the first time I've had some proper PCBs made, and I have a nagging doubt about whether I need to be concerned about my drill sizes.The patterns/footprints for all the through-hole components I've been using have mostly been straight from my software's default library, without modification. And for a few other uncommon components, I've followed the exact dimensions the manufacturer recommends in their datasheet. As a result, I have a wide variety of through-hole diameters - 16 distinct sizes in all.It is my understanding that most of these Chinese board manufacturers only use metric drill sizes, potentially ranged in 0.05mm increments (although that's a guess, as hardly any of them specifically state that info). I presume, if presented with a drill file with non-metric sizes, they perform some kind of 'normalisation' process to convert the hole sizes to match the metric tooling they have? Does anyone have insight into what they generally do? Would they just round the sizes up to the next 0.05mm increment?

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: March 21, 2016, 03:58:12 pm
content: I think probably the only useful answer you will get to this question will be from the board house that you want to use. If they don't state maximum number of drill sizes or the tolerance for their holes in their design rules, you will have to ask them.

author: Aodhan145
author_rank: Frequent Contributor
timestamp: March 21, 2016, 04:25:44 pm
content: Shenzhen2U are cheap I used them with my latest batchhttp://www.shenzhen2u.com/. You should use pcbshopper which is a price comparison tool between most cheap Chinese fabshttp://pcbshopper.com/

author: jitter
author_rank: Frequent Contributor
timestamp: March 22, 2016, 11:22:53 am
content: Quote from: Aodhan145 on March 21, 2016, 04:25:44 pmHow does this answer the original question?I agree with Denzil, find a boardhouse that you can communicate with and ask.

author: Aodhan145
author_rank: Frequent Contributor
timestamp: March 22, 2016, 05:20:43 pm
content: Quote from: jitter on March 22, 2016, 11:22:53 amYeah he needs a boardhouse though. I was just recommending some.

author: djQUAN
author_rank: Frequent Contributor
timestamp: March 22, 2016, 05:28:55 pm
content: I use PCB cart and don't really pay attention to hole sizes in my layouts.In my case, I upload the Eagle file directly and they send a PDF for verification before it is manufactured.In all cases, they did change the holes to more common bit sizes that they have.

author: ChunkyPastaSauce
author_rank: Unknown
timestamp: March 22, 2016, 05:50:34 pm
content: Real answer.... is yes and noAny legitimate PCB (or anything else) manufacture will size to exactly what you specify.....to within the tolerance that is stated for work.So if you specify a 1mm hole and the stated tolerance is +-0.05mm you will get a hole that is 0.95-1.05mm. The tool they pick is up to them, as long as it meets the specs, you specify 1mm hole, and for some reason they only have a 1.025mm dill, you will get a 1.025mm hole... but it's within spec so is fine.When you specify 1mm hole, that is the nominal hole size (not actual), the actually hole size is the nominal+tolerance. They do 'normalize' (so yes), but should be within spec (so no).When you go bargain without specified tolerances, then it's up in the air.

author: IconicPCB
author_rank: Super Contributor
timestamp: March 22, 2016, 07:23:28 pm
content: We manufacture boards.Generally we will look at the drill fileand drill larger than specified holes.Typically 0.05 to0.1mm larger depending on the final thickness of copper..If the specified copper finish is say 2 ounces (per square foot) or 70 micron we will go oversize by 0.1mm to accommodate the greater plating thickness inside the holes.We carry drill bits from 0.3mm to1.6mm in increments of 0.05mm. Larger holes are converted to milled outlines and milled out with a 1mm router bit having benefited from similar expansion rule.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: March 22, 2016, 08:26:23 pm
content: Thanks for the info.I did already understand that the actual physical holes drilled will be enlarged so that after the plating is applied the finished diameter will be back to what was originally specified (or as near as possible). It was just the business of how a manufacturer would normalise the sizes to their available tooling that concerned me. I suppose you guys are right in that the only real way of finding out exactly will be to ask, but it's good to know that a size increment of 0.05mm is common. Most of these Chinese manufacturers only state what the bounds of their size range are (e.g. "0.3 up to 6.3mm"), which was frustrating.I actually figured I could do the maths and work out if any rounding-up or rounding-down would have any significant impact. Taking a rounding up/down to nearest 0.05mm, it actually came out that the largest difference either way among my assortment of hole sizes would be 2 thou, which shouldn't cause any problems for the diameters of annular rings I have. So I guess nothing to worry about really after all.Oh, and finally, no, I wasn't in need of any recommendations for board manufacturers.