The IPC now has a formatting document with General PWB Design Guidelines that anybody can use as a template for their company's controlling PWB Design rules document. The IPC is the first in line to acknowledge that no standard can control every aspect of a design or fabrication rule.
I have written several of these PWB Design Rules or PWB Acceptance documents for many different companies (even though I am not strictly a design engineer), and within that document I have outlined the company's philosophy for minor changes that occur as a result of autorouting or trace optimization. Usually, the customer company wants at least some notification of etch factors, autoroute changes, etc., so they can make sure that these will not affect the performance of the finished CCA (what seems relatively minor to a PWB fabricator can be a great big showstopper for the user).
Something like this is invaluable; you cannot detail everything on the PWB Fab drawing.
dean
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Nowak, Ronald
Sent: Friday, March 20, 2015 12:44 PM
To: [log in to unmask]
Subject: Re: [DC] EXTERNAL: [DC] ???: Re: [DC] Question of the Week - Teardropping
Yes they do. These are called etch factors, or compensation factors. So if the design data reflects a 4 mil (100um) wide trace, the artwork generator may actually expose a trace that is significantly larger than 4 mils. This line is then patterned with a DES process (develop, etch, strip) that should have it at 4 mils after being etched, provided the manufacturer know his process. Compensation or etch factors will be affected by weight or thickness of the Cu, the spacing between the lines, among other things. These factors are often adjusted after the first job or two is run to dial in closer to the designed trace width.
On the other hand, if you manufacturer is moving traces or vias in your design without your consent, you may have a problem, especially for impedance controlled lines or traces that have skew requirements on them for timing. These are items that should be resolved with you fabricator before the PCB is released to the line. Some manufacturers may enlarge signal capture pads to help with registration. I would suggest that you speak early and often with your supplier to understand what he does through his front end CAM process.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Shalom Shlomi Zigdon ????? ?????????? ?????
Sent: Friday, March 20, 2015 11:06 AM
To: [log in to unmask]
Subject: EXTERNAL: [DC] ???: Re: [DC] Question of the Week - Teardropping
i hope you all know that most of manufacturers are making changes in your gerber files without asking a permision.
???? ????????? ?-Samsung Galaxy ???.
-------- ????? ?????? --------
???: Bob Wilson <[log in to unmask]>
?????:2015/03/20 7:59 AM (GMT-08:00)
??: [log in to unmask]
????:
????: Re: [DC] Question of the Week - Teardropping
I give the fab an option like, teardrops may be added as long as space restrictions are met. Adding them dies increase yield. You have to find a fab that will tell you the truth even though you're a 'customer'
On Mar 19, 2015 9:42 PM, "Frank Kimmey" < [log in to unmask]> wrote:
> Jack,
> I guess I am a loner.
> I don't teardrop anything.
> Teardrops and Snowmen are safety measures from the days when fab was
> not as well controlled with good process and chemistries.
> I make sure there is good annular rings and not had a breakout
> experience in well over 10 years.
> I have moved on from RF to HS and seem to have no issues yet.
> As always I will stand by working with your Fabricator and make sure
> your designs are well within their capabilities.
> If you do your up front, do you really need a belt with your suspenders?
> I am not trying to say teardroping is bad, rather that I want every
> bit of routing space I can get.
> As always we need to look at what gives the closest to our needs.
> If you have the space and time, then do whatever you can to armor plate.
> If you don't need then why take the added time they take.
> Just how I see it.
> Let us know if the fog clears,
> FNK
>
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