James,
I must agree with your statement but I feel I should clarify my original response regarding the comment about board shops not being able to maintain the 2 mg/sq. in. The key is maintaining. To maintain this requirement on any given lot of product consistently will typically require an added special cleaning step. Perhaps more than one. This will add costs to the board which most customers are not happy to hear about. In addition, as noted in my original response, my experience stemmed from one of our customers using a heated bath during testing. Our internal test results after our standard ionic cleaning process didn't even register any contamination after 10 minutes. Yet my customer showed in excess 4 mg/sq. in on a random sample. Although it did not result in a rejection, my customer was concerned because our certification data didn't match what they were getting. I am sure the requirement can be maintained with the appropriate cleaning process. But at what cost?
By the way, is this 2 mg / sq. in. becoming a more prevalent requirement in today's market?
I need to know this so I can get a jump on the equipment needed to test it to that degree.
All responses will be appreciated.
Thank you,
Ed Cosper
[log in to unmask]
----------
From: Maguire, James F[SMTP:[log in to unmask]]
Sent: Tuesday, March 04, 1997 9:33 AM
To: 'Ed Cosper'
Subject: RE: No Clean Bare Board Controls
Actually, our in-house requirement is 2 micrograms/square inch and it
can be met (and even if failed we don't scrap, we re-clean and retest).
I would note though that we test with an older (unheated) type extract
system (OK, it's an Omegameter 600). We've had some limited experience
with the newer, heated systems (actually we're buying one) and
indications are that for a given PWB the newer, heated systems can read
>> higher levels of contamination than the older (unheated/static)
systems. I would agree that it may be difficult to meet the 2
microgram/in^2 requirement on a newer system.
Note that the IPC methods (static vs. dynamic) don't specify heated or
not but your in-house spec should in order to avoid confusion.
===============================
Jim Maguire
Senior Principal Engineer
Boeing Defense & Space Group
(206)657-9063 fax 657-8903
Email: [log in to unmask]
================================
>----------
>From: Ed Cosper[SMTP:[log in to unmask]]
>Sent: Monday, March 03, 1997 3:44 PM
>To: 'Davis, Mary'
>Cc: [log in to unmask]
>Subject: RE: No Clean Bare Board Controls
>
>Mary,
>
>Are you sure you mean 2 mg/sq. in. or do you mean 2 mg/sq. cm? Even Bell Corp
>allows 7 mg/sq. in. I'm not sure a bare board supplier can maintain 2 mg/sq.
>in if any type of soldermask is used. This is a very tight requirement. If
>you specify this requirement, I would recommend adding a statement such as "
>when tested in accordance to .....". This will specify the type of testing
>required and eliminate any potential correlation problems in the future.
>There is a variation in results based on test method. The most recent issue I
>had to deal with stemmed from my not using a heated solution vs my customer
>using a heated solution.
>
>If you stipulate an LPI, I don't think you need to specify a brand. As for as
>test method, specify the same method and chemicals you intend to use to
>verify the parts at receiving. Once you have stated the requirements and
>test methods, the supplier should be able to choose a mask that will meet
>those requirements . Just my thoughts.
>
>Ed Cosper
>Director, Quality Assurance and Engineering
>Graphic Electronics Inc.
>
>----------
>From: Davis, Mary[SMTP:[log in to unmask]]
>Sent: Monday, March 03, 1997 2:04 PM
>To: TechNet
>Subject: No Clean Bare Board Controls
>
>I would appreciate some guidance on a subject that could be of interest
>to others in the same dilemma.
>
>We are specifying controls for unpopulated PWB's to be used in low
>residue/no clean process. We plan to restrict bare board bulk ionic
>levels to no more than 2 micrograms/sq.in. NaCl equivalent. Also, it
>has been suggested that we require that 'polyethylene glycol substances,
>as well as certain dry film and even some liquid photoimageable masks be
>avoided'. The bulk ionic requirement is easy to communicate but I am
>struggling with the verbiage and test methods that describe restrictions
>on polyethylene glycol substances and other potentially harmful
>materials.
>
>Any help in this matter will be greatly appreciated.
>
>Mary Davis
>Sr. Material & Process Engineer
>Hughes Aircraft
>Naval & Maritime Systems
>206-356-3311
>[log in to unmask]
>
>
>
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