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March 2009

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Sun, 15 Mar 2009 15:19:14 +0000
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There are some key points to make. 

 - Your hands are washed 6-10 times a day and would overall be cleaner than any glove.   

- Proper handling is paramount where you handle the boards from the board edges. Most of the time before and after SMT reflow the  boards are still in panels with break-away rails so the boards are never touched. 

- The biggest issue I've had is with OSP boards in the pre-wave prep. The person applying kapton tape masking must use a wooden or plastic stick or finger cots to avoid contact with the board as they press the tape down to make the required seal. 



On Enig and HASL boards we insist that only a designated person applies the tape and that person washes their hands everytime they come back from break, before they start tape masking.  

After reflow, AOI and wave or selective solder the boards are depaneled. 

However the majority of the soldering has been completed and the boards are washed so the small chance of someone contaminating a pad or annular ring, reducing wetting is mute. 

With gloves you can't handle nor load small parts pre-wave and the gloves are going to pick up everything on the bottom of ESD trays, racks, benches, ESD parts bins etc. The cost to benefit ratio, including assembly efficiency is just not there. 



-  The customer and integrator is not going to be wearing gloves when they handle boards. 

- A finger print on the epoxy mask is not a reliability issue and has never been a defect in the cleanliness standard in IPC-A-610. 

Proper board handling, process control and training is far more effective than just spending lots of money on gloves which would  have collect every contaminate  and slow down the assembly process. 

John Goulet  Process Engineer 
----- Original Message ----- 
From: "Mike Fenner" <[log in to unmask]> 
To: [log in to unmask] 
Sent: Thursday, March 5, 2009 4:31:41 AM GMT -05:00 US/Canada Eastern 
Subject: Re: [TN] Gloved Hands / Fingerprints / Failure Articles 

Well.... Dirty money and that. 
Coins are usually thought of as being dirty having been through lots of 
hands, but in those made from copper alloys the bug count is actually low. 
Not so with the folding stuff! 

Regards 
  
  
Mike 
-----Original Message----- 
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Dixon 
Sent: Wednesday, March 04, 2009 3:46 PM 
To: [log in to unmask] 
Subject: Re: [TN] Gloved Hands / Fingerprints / Failure Articles 

I totally agree with Doug.  I mentioned this several years ago on this 
forum.....and feel it is safe to repeat now! 

I went to a fast food place and the guy running the cash register was 
wearing gloves...  How nice since that money is really filthy...  Then 
he walked over to the kitchen and prepared my food while wearing those 
same gloves!  I lost my appetite! 
Regards, 
Dave 


-----Original Message----- 
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D. 
Sent: Wednesday, March 04, 2009 8:50 AM 
To: [log in to unmask] 
Subject: Re: Gloved Hands / Fingerprints / Failure Articles 

Excellent, practical, pragmatic advice. Worth its weight in Mountain 
Dew. 

-----Original Message----- 
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls 
Sent: Wednesday, March 04, 2009 8:44 AM 
To: [log in to unmask] 
Subject: Re: [TN] Gloved Hands / Fingerprints / Failure Articles 

Kevin, 
I will throw in my two cents worth.  We do not wear gloves in our 
facilities for most of the manufacturing process.  They do in the clean 
rooms and they do after final wash prior to conformal coat.  The rest of 
the time it is, in my opinion, a waste of time and money.  Kind of an 
odd statement coming from me, but here is why I think so. 

Gloves are there to prevent finger salts and oils from getting on the 
assembly, where they would be a contamination risk.  Our cleaning 
processes are such that the last cleaning step is a mild one designed to 
remove such salts and oils.  The heavier residues have already been 
removed in previous process steps.  So, gloves are not really needed. 

Here is why I think it is a waste of money to have gloves on anywhere 
earlier in the process.  The assumption that gloves keep your assemblies 
clean is only true while the gloves themselves are clean.  Run your 
gloved hands through your hair.  New gloves.  Touch a little of that 
uncured adhesive.  New gloves.  Get a little flux from hand soldering on 
the gloves.  New gloves.  You think that the operators are going to 
change gloves that often?  No.  Think the manager for that area is going 
to willingly pay for the truckloads of new gloves.  Hell no.  In some of 
our areas, the operators that apply silicone RTV adhesive to the boards 
wear gloves because that RTV is hard to get off your hands.  Think they 
change them often?  Nope.  When the boards get to conformal coating, 
there are lots of dewet areas that mysteriously resemble fingerprint 
sized areas, but without the convenient identifying fingerprints.  Even 
though we stress to our operators to handle boards by the edges only, it 
is sometimes just not practical to do so.  Then again, since we have 
that final clean prior to coating, it is not as critical. 

Now, if you are a true no-clean facility, that is another issue.  If you 
go the route of gloves, I would recommend you stay away from finger cots 
and plastic gloves.  They are uncomfortable and when you make the 
operators uncomfortable, bad things happen.  I would highly recommend 
the use of HyFlex gloves, which you can get from Techni-Tool.  These are 
cotton gloves with heavier rubberized palms and fingers, but the back 
sides of the fingers and back side of the hand are open cotton, allowing 
the gloves to breathe. Very comfortable, good tactical feel to them and 
the surface is robust enough that you can clean off residues with mild 
alcohol so they last for a long time.  They cost a little more, but they 
are worth the investment considering their cleanability and how long 
they last. 

Doug Pauls 
Rockwell Collins 

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