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October 2000

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From:
Ken Patel <[log in to unmask]>
Date:
Mon, 9 Oct 2000 09:27:41 -0700
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"TechNet E-Mail Forum." <[log in to unmask]>, Ken Patel <[log in to unmask]>
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Do you think it will help in reducing tomb-stoning for many 0402 size
components by having few scattered local fiducials in the middle of large
board, say 11x17?


re,
ken patel

-----Original Message-----
From: Jim Kittel [mailto:[log in to unmask]]
Sent: Monday, October 09, 2000 5:08 AM
To: [log in to unmask]
Subject: Re: [TN] Fiducials and HDI


Thanks Poh,
Sounds like good data.
Jim Kittel

 -----Original Message-----
From:   Poh Kong Hui [mailto:[log in to unmask]]
Sent:   Friday, October 06, 2000 5:33 PM
To:     [log in to unmask]
Subject:        Re: [TN] Fiducials and HDI

Hi All,

I would like to make some comments. I ever had cases that some
assembly guys wanted the designer to put local fiducial when using
50 mil pitch BGA.

We evaluated using the placement machine to check the balls of the
BGA to perform centering vs using the component's outline of the
BGA to perform centering, it did not showed any difference.

However, I would like to say that local fiducial is rather critical
for the large board size if there is fine pitch component of 20 mil
pitch or less.

I encountered case that misalignment on 20 mil fine-pitch on the
board size of about 14 X 16 inches. It was alright once I used
local fiducial.

I would think it depends on situation of when we need to have local
fiducial or not.

Regards,
Poh


---------------------------------------------------------------------




At 01:05 PM 10/5/00 -0400, Paul Fly wrote:
>From: Paul M Fly
>
>Hi gang,
>
>  I have to make a few comments here. The company I work for is now working
>with a contract
>manufacturer for our PCB assembly needs. We used to have an in-house
>assembly operation,
>but they went out of business a year or two ago.
>
>  When we had the in-house assembly going we were required to put local
>fiducials on fine pitch
>SMT parts. Our definition of fine pitch being less than 25 mils. On a tight
>board getting those local
>fiducials in place could be a real problem, but we could generally find a
>way to make it work.
>
> Then our in-house group goes out of business and we are told to use the
>contract manufacturer.
>They want us to put local fiducials on regular 50 mil pitch BGAs! Steve I
>gotta tell you  Jim is 150%
>right, we are being pushed to make boards smaller but at the same time we
>are getting pressure
>for local fiducials in addition to global fiducials and thats on parts that
>our own assembly group could
>place two years ago using just the global fiducials! Sorry to sound like
>I'm venting (well maybe I am a little),
>but this trend I've been seeing is moving in the wrong direction.
>
>  Jim, to answer your question, yes we have been able to group parts into
>clusters and share fiducials.
>We have been given a dimension, (which I imagine varys from vendor to
>vendor) that we are told as
>long as the parts all fall within this distance from the fiducial it is ok
>to share a fiducial with several parts.
>
>Thanks for listening,
>Paul Fly
>
>
>
>
>
>"Stephen R. Gregory" <[log in to unmask]> on 10/05/2000 12:04:35 PM
>
>Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
>      to [log in to unmask]
>
>To:   [log in to unmask]
>cc:    (bcc: Paul M Fly/243609/EKC)
>Subject:  Re: [TN] Fiducials and HDI
>
>
>
>
>In a message dated 10/05/2000 9:55:18 AM Central Daylight Time,
>[log in to unmask] writes:
>
>Hi Jim!
>
>I'd have to agree with Daan. Very rarely, if ever, have I used local
>fiducials.
>
>As long as there is some good global fiducials, I've never found the need
>to
>use Locals...this includes placing 15.7-mil pitch parts and MicroBGA's...
>
>-Steve Gregory-
>
>> Hi Jim,
>>
>>  One solution could be to place the local fiducials underneath the
>components.
>>  Another solution: don't use them.
>>  And do you really need a 0.150 (inch ?) keep out area ?
>>
>>  Kind regards,
>>
>>  Daan Terstegge
>>  SMT Centre
>>  Signaal Communications
>>  Unclassified mail
>>  Personal Website: http://www.smtinfo.net
>>
>>  >>> Jim Kittel <[log in to unmask]> 10/05 3:25 pm >>>
>>  TechNetters,
>>
>>  With so much emphasis on reducing circuit board feature sizes by use of
>>  micro BGA's, micro lead frames, micro vias, etc. the use of local
>fiducials
>>  becomes a real burden.  For example, our typical fiducial is a 0.048
>circle
>>  with a 0.150 keep out area.  This keep out area is approaching the size
>of
>>  flash memories, micro BGA's, 0402 chips, etc.
>>
>>  Has anyone figured out a way to work around this local fiducial problem?
>Is
>>  anyone grouping these parts into some kind of symmetric clusters?  Any
>>  ideas?
>>
>>  Jim Kittel
>
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