My experience indicates that nitrile gloves vary greatly from brand to brand, grade to grade, etc., and testing should be performed to qualify them prior to use. I wasn't dealing with silver corrosion - but instead with transfer of residue that caused de-wetting of urethane conformal coating and cure inhibition of silicones. I was told by a rep from the glove company that the residue transfer was the result of residual un-reacted nitrile. That seems to make sense as nitriles are listed as a source of silicone cure inhibition.
Some nitrile gloves are washed as part of their manufacture. Some nitrile gloves are certified as containing low ionic extractable content. The washed and low ionic extractable gloves are relatively expensive but performed the best and prevented costly quality issues. And, once you get a nitrile glove product that is confirmed acceptable, you need to lock in your choice. Otherwise, time goes by and a buyer changes to a less expensive glove - and the quality problems return.
Regards,
Mary Davis
Retired Materials and Process Engineer
-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Joe Russeau
Sent: Tuesday, January 14, 2020 8:53 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] Need advice : sulphur level on Gloves/ESD mat and reference standards
I would add to this conversation by saying that we have tested power-free nitrile and powder-free vinyl gloves using ion chromatography for "ionic" contaminates. We analyze the lots of gloves we use to handle customer product to ascertain the types and amounts of ionics that we may be contributing to the test results. We have typically found that gloves of those types have very low levels of ionic contaminates (less than 1.5 ppm total for a pair of gloves anions and cations combined). Couple low ionic levels with proper handling techniques and you can minimize the chance for transference to a product.
That all said, I can't speak to the relative amounts of contaminates coming from ESD mats. Until this past year, ESD mats haven't really been on anyone's radar for being a corrosion contributor. Now there seems to be a lot of questions being asked about the levels of contaminates coming from mats and do those contaminates lead to corrosion products. To date, I am not personally aware of any standard that defines what contaminate levels ought to be for mats. Perhaps some guidance is needed. My 2 cents would when in doubt have those materials
tested, if for nothing else but peace of mind.
Best Regards,
Joe Russeau
PAL, Inc.
On 2020-01-14 10:55, David Hillman wrote:
> Hi team - I'll just add a couple of comments to the conversation. The
> tarnish typically found on immersion silver board finishes is the
> result of boards being wet/damp from processing which leads to a
> brown/black visual tarnish due to reactions with the air. The majority
> of the time the tarnish is cosmetic and does not impact the
> solderability of the board. If it is not cosmetic then you will find
> the solderability is a problem pretty easily. The gloves we use are
> not sulfur free - they are Micro Grip nitrile gloves from VWR
> International (part number 40101-350) and we haven't seen an issue
> with them causing tarnishing. Of course, everyone should be handling a
> board by its edges as much as possible too. I would look at your board
> storage and handling practices as possible root cause sources for the tarnishing. Good luck.
>
> Dave Hillman
> Collins Aerospace
>
> On Tue, Jan 14, 2020 at 7:42 AM Douglas Pauls <
> [log in to unmask]> wrote:
>
> "Last Century"? Thanks for turning me from old to ancient Bev.
>
> As Bev indicated, there are no standards in our industry for this kind
> of thing. The recommended ionic levels from Foresite, PAL, or other
> test labs are for circuit assemblies or bare circuit boards, not for
> amounts in gloves. We use standard latex or nitrile gloves here and a
> lot of what we use is immersion silver. We have not seen the need for special gloves.
>
> In terms of functional impact, if it is just tarnish, then there is no
> functional impact. Silver oxide conducts as well as pure silver. All
> you have is a cosmetic issue when people collectively lose their minds
> looking at tarnished silver.
>
> I suspect what happened is somebody somewhere thought "sulfur is bad
> for silver" (which it is), "so we need sulfur free gloves" (which you don't).
>
> *Douglas Pauls *| Principal Materials and Process Engr | Advanced
> Operations Engineering
>
> *COLLINS AEROSPACE*
>
> 400 Collins Road NE, MS 108-101, Cedar Rapids, IA 52498 USA
>
> *Tel:* +1 319 295 2109 | *Mobile: *+1 319 431 3773
>
> [log in to unmask]
>
> [log in to unmask] for all Export Compliant Items
>
> On Tue, Jan 14, 2020 at 7:31 AM Bev Christian <[log in to unmask]:
>
> First, do you like to be call GA or Tan?
> a) & b) There are no standards. Shoot, we don't have any "official"
> standards for sodium, potassium, fluoride, chloride, bromide, nitrate,
> nitrate, phosphate or sulfate; unless they are in IEC standards that I
> don't know about. We have the suggestions of Doug and Terry from the
> last century and those from Delco and a couple of other sets.
> Certainly the measurement of Doug Pauls, etc. are professionally
> carried out.
> c) Only cosmetic
>
> I have never heard anyone ask for sulfur free gloves. I am not aware
> of what is available. I would start with asking a VWR or Fisher rep
> (large chemical suppliers with extensive catalogues) .
>
> Regards,
> Bev
>
> -----Original Message-----
> From: TechNet <[log in to unmask]> On Behalf Of Tan Geok Ang
> Sent: January 14, 2020 6:34 AM
> To: [log in to unmask]
> Subject: [TN] Need advice : sulphur level on Gloves/ESD mat and
> reference standards
>
> Will really appreciate advice on the following;
>
> a) how much of sulphur/calcium, etc. on gloves/ESD Mat is acceptable
> and what level is considered harmful in handling of PCBA/module with
> sliver plated surface
>
> b) whether there are any "standards" or references for "compliance"
> check for sulphur, and is there such measurements professionally
> carried out
>
> c) What will be the impacts on the PCBA when silver plating become tarnish?
>
> There are sulphur free gloves but it is not easily accessible/available in Singapore and it is expensive.
>
> Thanks.
>
> GA Tan
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