Acid traps - Page 1
Forum section: electronics / general

author: IconicPCB
author_rank: Super Contributor
timestamp: February 14, 2016, 08:55:14 pm
content: What are recommendations for the minimum acute angle between two tracks to avoid /eliminate/minimise acid traps?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 14, 2016, 10:59:39 pm
content: I stick to <= 90 degrees, as much for aesthetics as anything. I don't know that acid trapping is a problem these days.The most common change request I see is the addition of teardrops (when moving into production). This is for drilling tolerance (ensuring annular ring around the hole, and connectivity), not etching.Tim

author: HWgeek
author_rank: Contributor
timestamp: February 27, 2016, 11:47:30 pm
content: Altium under 14.2.5 (rules might have changed for 15 and 16, haven't played with 16 much yet) had a bad habit of drawing traces that were 89 degrees or so.We would set acute to 90 and if any traces were routed before the rule was set, they invariably were like 89 degrees or so. Answer was to do 90, check for gross errors and then set for 85 degrees.Most of the errors seemed to be trace going to via and being just slightly, very slightly off. Would take more time to adjust than to worth. If you set acute first it seems to draw correctly, most of the time. :-)Several CM's have indicated that the newer processes don't cause acid trapping and continued etching like in the "old days".Certainly 90 looks nicer, and we work to make sure our designs are technically correct and also look clean. Nothing worse than doing a PCB review and seeing rookie routing that looks like a bowl of spaghetti. bleh.

author: uncle_bob
author_rank: Unknown
timestamp: February 28, 2016, 01:24:45 am
content: Quote from: IconicPCB on February 14, 2016, 08:55:14 pmHiI have not seen a comment about this on any design for about the last 10 years or so. I would not worry about it unless you have a board fab that is stuck in some sort of time warp.Bob

author: D3f1ant
author_rank: Frequent Contributor
timestamp: March 01, 2016, 04:03:08 am
content: Its extremely rare for this to be problem, but can still happen. Its not actually the etching acid that causes a problem,its the plating chemicals. Result is if board is not washed correctly, a hairline erosion occurs right at the edge of the soldermask, impossible to see unless you scrape it away. It also can take days or weeks to fail, so even fully tested boards can be affected.My board manufacturer accepted responsibility, explained how it can happen and replaced the boards, but it might have been preventable with a click of the add teardrops button.

author: mobbarley
author_rank: Regular Contributor
timestamp: March 01, 2016, 08:52:12 pm
content: I've also found this exceedingly rare, good to see the pictures above.I supposed minor defects can easily go unnoticed under the mask?

author: IconicPCB
author_rank: Super Contributor
timestamp: March 01, 2016, 10:24:05 pm
content: The reason behind the question is as follows.I make boards using mechanical milling process.Ideally to keep costs down an isolation pass around the connected copper should be sufficient unless the design calls for a particular geometry.Often however end users request photographically correct product. By that i mean a board which looks like a photo tool exposed etched board.This of course implies rubbing out copper areas. In order to be effective and free of copper slivers adjacent tool paths need to overlap. This is not a problem in large open areas however adjusting / selecting tool diameter and or tool overlap in included areas within acute angles can be a problem.So in order to define the problem the question of just how acute the angle should be permitted to be is the real question.Hence the acid trap question or why bother to reinvent the angle.

author: uncle_bob
author_rank: Unknown
timestamp: March 02, 2016, 02:22:14 am
content: Quote from: IconicPCB on March 01, 2016, 10:24:05 pmHiIf you are using any sort of normal tool for machining the board, the radius of the tool will be larger than any "acid trap" ever was. If you want to be exact to the photo plot, then you need perfect "straight line" angles down to about 0.02 mm on some boards.Bob

author: IconicPCB
author_rank: Super Contributor
timestamp: March 02, 2016, 03:19:08 am
content: Hey uncle Bob,I am using macro tools starting with 0.4mm end mill bits and ending up in 2mm area. ( in imperial units 0.016" to 0.080")Below that I am using 0.0039" to 0.010" 15 degree cutters. ( in civilised units thats 0.1mm to 0.254mm )As you can see almost perfection.