Re: gEDA-user: Interesting board defect

[Steven Michalske <smichalske@xxxxxxxxx>]

On Feb 16, 2009, at 12:11 PM, Stefan Salewski wrote:

> Am Montag, den 16.02.2009, 18:53 +0000 schrieb Kai-Martin Knaak:
>>
>> Some remarks:
>>
>> * 4 Layers will take 12 working days minimum, plus what ever it  
>> takes for
>> fedex to ship from china. If you don't register for "open account"
>> payment needs to be confirmed before production time begins.
>>
>
> Yes, boards from china will take some time.
>
>> * Shipping and customs and EUSt have to be added on top of the quoted
>> price.
>>
>
> Yes, but total costs are still not bad. If I remember correctly: Four
> boards, 4 layer, each 26cm * 32cm will give total something about 1000
> Dollar. The only company which I aware of here in Germany which is not
> much more expensive is http://www.microcirtec.de
> Large quantities are really cheap at pcbcart, so I think it is a good
> idea to try them.
>
>> * There is a maximum number of holes. (300 for my 100x100mm test  
>> case)
>>
>
> I think this is no problem, most people use at least some SMD.
>
>> * Design rules are modestly aggressive:
>> 	minimum drill = 0.4 mm
>>  	minimum track width, minimum spacing = 0.2 mm
>>        minimum annular ring = 0.25 mm
>>  My preferred fab offers about 0.75 times these values as standard.
>>
>> * Poor english on the webpage. E.g: "For small quantity, if by air  
>> the
>> extra cost will make it not save" (no full stop).
>>
>
> My english is poor also -- perfect fit :-)
>
> I think their parameters are not too bad, and I think they can do
> better, for more money. (And I think drill is 0.3mm without additional
> costs, think I have seen it...)
>
>>
>>> I think they have no information for impedance control on their page
>>
>> There is an item "impedance control" in their quote. I'd guess, this
>> could be set this to some other value on request.
>>
>
> I have seen this, but do not understand it.
>
> I have asked by email some months ago, and got only a very short  
> reply:
>
>> Hi Mr. Salewski,
>
>> Thanks for your suggestion, we are considering improving our  
>> homepage.
>> Regarding to your question, please see follows:
>> Trace width: 8.5mil, 1oz copper, 0.12/1.13/0.12 for 50ohm impedance.
>> Best regards
>
> Not much. I guess that I will get 50 Ohm impedance for traces on outer
> layers of 4 layer board if trace width is 8.5 mil. Hope that I really
> will get this.
>

send then a "demo" board.

with your stack up and your trace, that you expect to be 50 Ohms.

and ask them to verify that their process will make that 50 Ohms.

We send "spec" boards to our vendors with test lines for our  
controlled impedances.

and they then verify that our assumptions about their process were  
right.

>
> Best regards
>
> Stefan Salewski
>
>
>
>
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