PCB copper defect? - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: March 09, 2017, 04:21:53 am
content: I came across an interesting effect on a PCB today. There seems to be small holes or voids in the copper, which at first I thought was micro via stitching, until I remembered it's a single-layer board. The effect is locally uniform, with centres at about 0.25 mm, but comes and goes in patches across the board.I assume this is a manufacturing defect, but does anyone know the mechanism that causes it?

author: Daixiwen
author_rank: Frequent Contributor
timestamp: March 09, 2017, 10:28:28 am
content: It looks like the PCB software generated a grid to fill the planes, with line widths that are not sufficient to cover the whole area. I remember some PCB software from 20 years ago that did this as default. If the clearance between two lines is below the minimum clearance the PCB manufacturer guarantees, you will get that kind of holes in the copper. The defect is not uniform because of variations of the focus resolution of the photo process. You get a better focus right under the light source, but if you are too offset on the side it will blur a bit and won't produce holes as big.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 09, 2017, 11:18:24 am
content: It may not be an error, but rather a choice. If you look at Eagle's polygon pour options for copper fill, you get a choice of solid, hatch or cutout.John

author: ar__systems
author_rank: Frequent Contributor
timestamp: March 09, 2017, 04:47:47 pm
content: Nope, does not look like it is was done on purpose. Looks like it is just exceptionally crappy PCB manufacturer. (Even if there was a defect in s/w creating tiny holes in polygons, they should've caught and fixed those.) Look at how jagged the diagonal trace in the left lower corner on the first pic is.I think the grid is caused by the FR4 material being uneven due to its woven structure, and poor exposure.

author: Erin.KOU
author_rank: Newbie
timestamp: March 14, 2017, 07:06:38 am
content: For this situation, Some times, it maybe a EQ that the fab will ask, if it need to make it being solid copper/ hatch copper. This is according to the engineering who take it as problem.But A suggestion that after you generating the Gerber files, it is better to review the Gerber files before you sent to the PCB fab.As only yourself who know the exactly need for your design.Erin KOU(sales manager,ALLPCB)

author: richardlawson1489
author_rank: Regular Contributor
timestamp: March 15, 2017, 10:47:21 am
content: Is Copper Thickness is reduced after PCB processing?

author: Erin.KOU
author_rank: Newbie
timestamp: March 16, 2017, 06:50:03 am
content: Quote from: richardlawson1489 on March 15, 2017, 10:47:21 amwhat do you mean for it?Do you mean the finished copper thickness?

author: HHaase
author_rank: Regular Contributor
timestamp: March 16, 2017, 02:55:36 pm
content: Definitely a defect and not an intentional fill pattern in this case. As mentioned, you can see the same pattern manifesting in the 45 degree trace on the bottom left. You can also see hints of the same pattern in the laminate between the traces too.My guess would just be poor quality laminate with the weaving coming through the surface resin.

author: wraper
author_rank: Unknown
timestamp: March 16, 2017, 03:03:07 pm
content: Quote from: ar__systems on March 09, 2017, 04:47:47 pmThat is very cheap crappy single layer PCB, therefore traces are not perfect.QuoteIf that was not intentional, then why those holes in the copper are located at regular pattern?

author: ar__systems
author_rank: Frequent Contributor
timestamp: March 16, 2017, 03:53:25 pm
content: Quote from: wraper on March 16, 2017, 03:03:07 pmI already said that.Quote from: wraper on March 16, 2017, 03:03:07 pmI already said that as well - I think it is pattern of FR4 fabric.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: March 16, 2017, 04:17:31 pm
content: I've seen this kind of thing occasionally, and never thought too much about it.It seems unlikely that it is the FR4 fabric weave since there is no trace of the defect in the narrow traces outside the large fill areas. A little work with a ruler or photo editing program shows that the weave pattern would definitely affect one or more of those traces. There are clearly two different phenomena going on since picture two shows both the rectilinear array of roundish holes and a row of rectangular holes aligned along a diagonal edge of the fill. Seems it has to be either an intentional or unintentional result of the gerber/mask creation process. Either way it doesn't look like it would affect functionality or yield of the board.