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April 2011

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Subject:
From:
Steve Gregory <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Gregory <[log in to unmask]>
Date:
Sat, 9 Apr 2011 23:16:36 -0400
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Race is over. Jr. didn't win. Oh well, what else is new?  >:^(

Pink bubbles. That might be cute I guess... :^}

But the problem is the 17" X 22" board dimensions. The biggest aluminum tray 
dimension that I've found is 18" X 26" O.D., which is the same dimension 
that Bliss has before it jumps up to a 20" X 26" tray cart. A 18" O.D. wide 
tray loses about 1.5 inches on the inside dimension where the board will 
actually lay upon, so our 17" wide boards won't work.

I have used aluminum bakers trays and carts a long time ago at the very 
first assembly company I worked at after I got out of the Navy. It was at 
Vantronics in San Jose (they aren't around anymore), and it seemed to be a 
good idea at the time. We were able to increase the storage space for the 
WIP over a small floor footprint, and move a lot of assemblies in the cart 
all at once. We were able to buy the trays and carts that came from a 
commercial bakery that went out of business for a song at an auction.

But after using them for a while, we started noticing black fingerprints on 
the assemblies, and at first weren't exactly sure where the prints were 
coming from. We then discovered that it was coming from the trays themselves 
after being slid in and out of the tray cart hundreds and hundreds of times. 
The aluminum starts wearing down at where the "L" bracket of the cart and 
the tray interface over time, and creates a very fine dust that is easily 
picked up on your fingers and transferred to anything that you touch.

It probably isn't an issue in a bakery environment because the trays are 
most likely washed after each use (at least I hope they are!).

So from that experience, I would like to stay away from aluminum trays and 
carts if I can. The Bliss carts are zinc plated steel and the trays are an 
ESD composite, so you don't see that kind of wear issue.

So the question still remains, does it really buy you anything to have an 
enclosed cart?

Steve

-----Original Message----- 
From: Joyce Koo
Sent: Saturday, April 09, 2011 8:41 PM
To: [log in to unmask]
Subject: Re: [TN] Class 0 ESDS board assembly transport...

Buy a aluminium baking try for thx giving with lid? :-) plus pink bubbles 
sure look cute.
--------------------------
Sent using BlackBerry


----- Original Message -----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Saturday, April 09, 2011 08:22 PM
To: [log in to unmask] <[log in to unmask]>
Subject: [TN] Class 0 ESDS board assembly transport...

Hi All,

Hope you all are having (or have had) a good weekend. I’m recovering from 
sort of bug that laid me low on Friday.

So today, I’m just taking it easy and have been searching around for the 
best solution to a project that we have, and that is trying to come up with 
a good way to move our board assemblies around on the production floor.

What makes this project a bit more complicated than what I’ve faced before, 
is that we need to be able to accommodate 17” X 22” boards (which we build a 
fair amount of), and we need to be thinking about Class 0 (100V) ESDS 
devices. Yep, they’re here now, and ya’ll will be seeing them in the future 
before too long. Here’s one that we’re starting to see now:

http://components.omron.com/components/web/PDFLIB.nsf/0/8B06D373BFF754C6862574FE007B0E26/$file/2SMES-01_1210.pdf

So, my first thought was Bliss tray carts. I’ve bought them in in the past 
at the other companies that I’ve worked at. In fact, Bliss has one of my old 
Technet postings on their web page recommending them. But I never had to 
deal with 17” X 22” boards and Class 0 ESDS devices before.

I thought that their 18” X 26” enclosed cart would work, but the boards won’t 
fit in their trays. The actual tray width at bottom inside dimension is only 
16.5 inches. So I have to go up to their next cart size, which is 20” X 26”, 
but they don’t offer the enclosed option like they do with the 18” X 26” 
cart. They will do custom stuff, but I’m sure that is going to add big $$$ 
to the cost.

So I have a multipart question ; if the cart is on conductive casters and 
rolling on a static dissipative floor, has good drag chains, the boards are 
on ESD trays, and assuming the person moving the cart is well grounded, does 
enclosing the carts offer significantly more protection? I know that having 
the board completely enclosed inside a faraday cage is ideal, but how can 
you practically accomplish that? Especially with boards as large as 17” X 
 22”?

I’ve even been looking at basic, enclosed stainless steel food delivery tray 
carts thinking that might be a solution, but had a cow at what they cost! I 
was looking for something that would handle anywhere from 10-20 trays, that 
I could put a 20” X 27” tray in, and they can go for anywhere from $2000 on 
up! That’s without the trays too...

After spending a good part of the afternoon looking for carts, ESD trays, 
and especially after reading this article:

http://circuitsassembly.com/cms/magazine/95/6351

I’m realizing what a task this is. It’s not just about the carts, but it is 
much, much more than that.

But for now though, I just need to figure out a good way to move our product 
on the production floor. I’m curious about how you all have addressed this.

I think I’m going to watch the NASCAR race now...

Steve

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