On Thu, 21 Apr 2016 02:12:26 -0700, raimond.dragomir wrote:> joi, 21 aprilie 2016, 12:08:14 UTC+3, David Brown a scris: >> On 21/04/16 11:01, raimond.dragomir@gmail.com wrote: >> >> >> > Specs in mm are annoying. Does anybody work in mm for pcb designing? >> > >> > >> Yes, most of the world does. >> >> Apart from Americans, I think it is just older Brits that use metric >> units for any sort of specifications. It is not uncommon to use mils >> for approximate numbers for track width and spacing, simply because you >> get nice numbers like 8 mil rather than 0.2 mm. But when you need >> accurate numbers, metric is how almost everyone outside the USA does >> it. > > Wow, I thought everybody works in mils for pcb designing... I'm not > american, but I work in mils for pcb layout since I started my career in > embedded systems, 20 years ago...That made a lot of sense with DIP and SOIC back then. But today's BGAs typically have ball pitches of 0.5, 0.8, 1.0mm etc. That doesn't work out to an even number of mils. Regards, Allan
Another PCB Fab Thread
Started by ●April 6, 2016
Reply by ●April 21, 20162016-04-21
Reply by ●April 21, 20162016-04-21
On 21/04/16 11:12, raimond.dragomir@gmail.com wrote:> joi, 21 aprilie 2016, 12:08:14 UTC+3, David Brown a scris: >> On 21/04/16 11:01, raimond.dragomir@gmail.com wrote: >> >>> >>> Specs in mm are annoying. Does anybody work in mm for pcb designing? >>> >> >> Yes, most of the world does. >> >> Apart from Americans, I think it is just older Brits that use metric >> units for any sort of specifications. It is not uncommon to use mils >> for approximate numbers for track width and spacing, simply because you >> get nice numbers like 8 mil rather than 0.2 mm. But when you need >> accurate numbers, metric is how almost everyone outside the USA does it. > > Wow, I thought everybody works in mils for pcb designing... > I'm not american, but I work in mils for pcb layout > since I started my career in embedded systems, 20 years ago... >Does that make you an older Brit? I don't do much pcb design, but I find mil sizes for tracks nice. But for everything else in pcb design, mm is the only way - it is the standard unit for parts, boards, holes, thicknesses, etc.
Reply by ●April 22, 20162016-04-22
On 4/21/2016 5:01 AM, raimond.dragomir@gmail.com wrote:> joi, 21 aprilie 2016, 09:47:08 UTC+3, rickman a scris: >> On 4/21/2016 2:06 AM, Reinhardt Behm wrote: >>> rickman wrote: >>> >>>> On 4/21/2016 1:16 AM, rickman wrote: >>>>> On 4/20/2016 11:48 PM, Paul Rubin wrote: >>>>>> Seeed Studio also has some cheap pcb fab: >>>>>> >>>>>> http://www.seeedstudio.com/depot/Services-c-70_71/ >>>>> >>>>> Yes, their prices are not bad, didn't check the specs. I was looking at >>>>> pricing options and they said it was +$30 to panelize 4 boards, but they >>>>> added $60 to the order. I guess they double the charge for 4 layer >>>>> boards. What's with that anyway? How do they have a higher cost for >>>>> panelized boards? >>>> >>>> I checked the specs and they get pretty sloppy for 4 layer boards. Not >>>> sure why the inner layers have worse trace/space than outer, but it's >>>> 8/10 mils. That's pretty poor. >>> >>> That is for 2oz copper. For the usual 1oz Cu it's 6 mil outer and 8 mil >>> inner layer. >>> <http://support.seeedstudio.com/knowledgebase/articles/447362-fusion-pcb- >>> specification> >>> Surcharge for panelized boards applies only if the boards are different. The >>> higher price is probably for the additional processing step for V-cuts. >> >> You misunderstand what I wrote. Inner layer is 8 mil trace, 10 mil >> space regardless of copper thickness. They list copper thickness of the >> outer layer as 1 or 2 oz and don't distinguish between these for the >> trace resolution. The inner layers are always 0.5 oz., so the inner >> layer trace width would not vary based on outer layer thickness. >> >> They also mix units between mm and mils as the selected unit for the >> spec. Example, Minimum inner trace width (for 4 layer) 0.204 mm, 8 mil. >> Drilling Hole Diameter (Mechanical) 0.3 mm, 11.81 mil. It would be >> nice if they used the same unit type as the primary units for all the >> specs. >> >> -- >> >> Rick > > Specs in mm are annoying. Does anybody work in mm for pcb designing?Yes, I do as much as possible. The problem comes from the small differences when using convenient sizes rather than exact equals. For example trace and space in mils are low, often single digit numbers, 6/6 is not uncommon. In metric that would be 0.1524/0.1524 which I would round down to 0.15/0.15 which helps in routing with many metric parts (aren't they all metric?) This should be perfectly manufacturable on any 6/6 process. Many PCB vendors check the design files with a program which flags many errors. So standardizing on metric would be big help. -- Rick
Reply by ●April 22, 20162016-04-22
On 4/21/2016 6:06 AM, Allan Herriman wrote:> On Thu, 21 Apr 2016 02:12:26 -0700, raimond.dragomir wrote: > >> joi, 21 aprilie 2016, 12:08:14 UTC+3, David Brown a scris: >>> On 21/04/16 11:01, raimond.dragomir@gmail.com wrote: >>> >>> >>>> Specs in mm are annoying. Does anybody work in mm for pcb designing? >>>> >>>> >>> Yes, most of the world does. >>> >>> Apart from Americans, I think it is just older Brits that use metric >>> units for any sort of specifications. It is not uncommon to use mils >>> for approximate numbers for track width and spacing, simply because you >>> get nice numbers like 8 mil rather than 0.2 mm. But when you need >>> accurate numbers, metric is how almost everyone outside the USA does >>> it. >> >> Wow, I thought everybody works in mils for pcb designing... I'm not >> american, but I work in mils for pcb layout since I started my career in >> embedded systems, 20 years ago... > > That made a lot of sense with DIP and SOIC back then. > > But today's BGAs typically have ball pitches of 0.5, 0.8, 1.0mm etc. > That doesn't work out to an even number of mils.That's a *big* problem with unit conversion. Inch to metric always converts exactly and with few additional digits because 1 inch = 25.4 mm. But 1 mm = 0.03937007874016... inches. The layout program I use internally uses nm because of this problem. Unfortunately it only allows mils to be used for trace widths. -- Rick
Reply by ●April 22, 20162016-04-22
On 4/21/2016 7:27 AM, David Brown wrote:> On 21/04/16 11:12, raimond.dragomir@gmail.com wrote: >> joi, 21 aprilie 2016, 12:08:14 UTC+3, David Brown a scris: >>> On 21/04/16 11:01, raimond.dragomir@gmail.com wrote: >>> >>>> >>>> Specs in mm are annoying. Does anybody work in mm for pcb designing? >>>> >>> >>> Yes, most of the world does. >>> >>> Apart from Americans, I think it is just older Brits that use metric >>> units for any sort of specifications. It is not uncommon to use mils >>> for approximate numbers for track width and spacing, simply because you >>> get nice numbers like 8 mil rather than 0.2 mm. But when you need >>> accurate numbers, metric is how almost everyone outside the USA does it. >> >> Wow, I thought everybody works in mils for pcb designing... >> I'm not american, but I work in mils for pcb layout >> since I started my career in embedded systems, 20 years ago... >> > > Does that make you an older Brit? I don't do much pcb design, but I > find mil sizes for tracks nice. But for everything else in pcb design, > mm is the only way - it is the standard unit for parts, boards, holes, > thicknesses, etc.I'm fine with giving up Mils for trace width/space. I'd happily give up ounces for thickness too. 1 oz = 0.035 mm. Is that really so hard? -- Rick
