Sealant based on my understanding is to fill a gap that may cause the ingress of harmful species; you need to know what are the two solid surfaces formed gap in between, how large the gap, what you try to protect with and for how long (assume you are not talking about infinity). And assume you provide a good selection that will keep the gap filled sufficiently during the life of the unit under full operation environment (not just some op environment). Encap, goes on top of something, your device, solder leads, for ex. The function is to provide intend support but not impede its function, hopefully enhance it. For example, encap on globtop, block UV, provide support for wirebond, enhance thermal properties if you select filler properly. Hopefully, it made a bit clear. My 1.96 cent.
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----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Tue Mar 30 08:54:03 2010
Subject: Re: [TN] Low Outgassing, Black Sealant / Underfill
Thank you, everyone, for the broad wealth of answers. I now have a few options to run-down, so thanks to all.
Joyce, you made a comment that prompts some thoughts - that encapsulants and sealants are two different things? I've considered that adhesives and sealants are different animals, and I understand that a sealant might not provide the structural support that an adhesive might, or an that an adhesive might not provide the moisture resistance a sealant might, but how do you consider that encapsulants and sealants vary? Is it simply a difference in viscosity, whereas an encapsulant might be thinner than a sealant and flow around / under items whereas as sealant would be thicker and allow sealing over gaps, holes, or around components? Would an underfill be considered more an encapsulant or a sealant?
Also, can anyone point out some background reading (papers) discussing when to underfill vs when to seal (or encapsulate)?
Thanks!
Kevin Glidden
Manufacturing Engineer
Astronics Luminescent Systems Inc.<http://www.astronics.com>
4 Lucent Drive
Lebanon, NH 03766
(603) 643-7766 x3152
________________________________
From: Glidden, Kevin
Sent: Monday, March 29, 2010 8:25 AM
To: 'TechNet E-Mail Forum'
Subject: Low Outgassing, Black Sealant / Underfill
Good Morning, and Happy Monday.
A couple of questions for anyone:
We have a lighting application where we are getting light reflection off two specific solder joints (we're so lucky to still use Sn63Pb37 they are just TOO shiny!), so I am looking for a method to cover those joints with a black (or dark gray) sealant. This would need to be a low out-gassing material. Does anyone know of any such material? Is there such a thing as black pigmented conformal coating?
The second question would be for this same product. I also have a need to seal around the base of some LEDs to prevent moisture ingress to the bottom only terminations. Would perimeter sealing be sufficient? How does one determine when they need to underfill vs perimeter seal?
Thanks!
Kevin Glidden
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