Graham,
Try EOS/ESD Society Advisory Docments WIP2.2- Garments Field Attenuation.
This eill cover test procedures for determing the electrostatic field
attenuation of garments. This society has a home page:
http://www.eosesd.org Let me know if you need more help.
Richard Haynes
609-497-4584
-----Original Message-----
From: Graham Naisbitt <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, October 16, 1998 12:43 PM
Subject: Re: [TN] Confomal coating adhesion
>Dear Mary and Paul,
>
>Interesting comments.
>
>Also I have found de-wetting and adhesion to be two separate issues.
>De-wetting, as you describe, is the effect seen when the coating is in a
>liquid form, before cure. We see de-wetting issues mainly with silicone
>contamination prior to coating.
>
>Adhesion is when the material is cured. In this instance a low surface
>energy of the coating is a bad thing and will lead to bad adhesion.
>
>Thus optimum is a low surface tension before cure, and a high surface
energy
>after cure.
>
>In this respect I don't agree with 'the lower the better' in terms of both
>requirements (no de-wetting and good post cure adhesion).
>
>As an example, a silicone conformal coating will wet just about anything,
>but it does not adhere well to a PCB surface. It may pass a cross hatch
>test, but only because the tape won't stick to it either! Silicone coatings
>are often flexible enough to induce only very low stresses from TCE
mismatch
>throughout the life of the board, and the low adhesion therefore doesn't
>manifest itself as delamination.
>
>We have done several studies of adhesion and de-wetting, and the issues
>involved range from free silicones (from heat transfer compounds, buffering
>materials and even mould release agents from component case moulding) to
>levelling agents in high gloss solder masks. Flux residues and reflow
>profile can also impact on localised adhesion.
>
>The result of our work is an adhesion modified coating material with no
>degradation in terms of wetting ability.
>
>In terms of thin edge coverage, application procedure is the key. Paul do
>you dip or spray? I have notes for optimising your application to minimise
>these effects if you wish to contact me off line I can mail them to you.
>
>Best Regards.
>
>Alan Brewin
>Chief Chemist - Concoat Ltd.
>
>-----Original Message-----
>From: Davis, Mary <[log in to unmask]>
>To: [log in to unmask] <[log in to unmask]>
>Date: 12 October 1998 17:54
>Subject: Re: [TN] Confomal coating adhesion
>
>
>>We found that success in wetting plastic packages very much depends on
>>the conformal coating material. Assuming the packages are clean and
>>free of oil and mold release, wetting is a function of the surface
>>tension of the coating material and the critical free energy of the
>>substrate. Some coating products have the appropriate surface tension
>>for plastic substrates, some do not. Talk with your coating manufacturer
>>and try various products. Do not assume that what worked elsewhere will
>>work on plastic. Some plastics have very low critical surface free
>>energies - in the range of 18-40 dyn/cm. Ask your coating manufacturers
>>if they can tell you the surface tension of their coating products. The
>>lower the better. If the surface tension of the coating is less than
>>the critical free energy of the solid, complete wetting will occur; but
>>if the surface tension is greater, partial non wetting can result.
>>
>>Call me and I can tell you the name of the product performed best in our
>>application.
>>
>>
>> Mary Davis
>> Sr. Material & Process Engineer
>> Product & Process Analysis Lab
>>
>> Raytheon Systems Company
>> Naval and Maritime Systems
>> KW 281, MK4C08
>> 6500 Harbour Heights Parkway
>> Mukilteo, WA 98275-4862
>> 425.356.3311
>> 425.356-3185 fax
>>
>>> -----Original Message-----
>>> From: Paul Stolar [SMTP:[log in to unmask]]
>>> Sent: Monday, October 12, 1998 7:09 AM
>>> To: [log in to unmask]
>>> Subject: [TN] Confomal coating adhesion
>>>
>>> Does anyone have any good experience at improving conformal
>>> coating
>>> adhesion to plastic packaging?
>>>
>>> Is it a cleanliness issue, or is it inherent in materials?
>>>
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