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January 1999

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From:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 4 Jan 1999 17:25:25 EST
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In a message dated 1/4/99 10:20:57 AM Pacific Standard Time,
[log in to unmask] writes:

<< Happy New Year TechNetters,

 Well, it is a new year and we want to try something new. I am interested in
 information and experiences on measuring the paste that has been applied;
 what equipment, difficult/easy for operators, benefits of use, etc.

 When you reply and if you are a CM, knowing that would be helpful.

 As in the past, thanks for any info in advance.

 Richard Hamilton
 Clemar Mfg. / Rain Bird
 [log in to unmask]>>

Happy New Year to You too!

    I don't know 'bout you, but didn't it seem like '98 just blew by? Did to
me. Last year was the year of the Tiger, and this year, it's the year of the
Rabbit...I wonder what that signifies? Have to consult with Elmer Fudd so he
can tell us something 'bout those "wascully wabbits"...hehehehehe.

    About solder paste measuring. I'm at a contract assembly company (start-
up), and we measure solder paste here. The jobs that we've had so far have
been mostly prototype and pilot runs of less than 100-boards, so we haven't
done any real SPC, just a good measurement on the first few boards after
initial printer set-up to verify that we're getting what we expected as far as
height goes, and then monitor the following prints under a loop magnifier at
the critical areas on the board (fine pitch, bga footprints).

     To be perfectly honest about things, until I experience a situation that
shows me otherwise, even if I had larger quantities of boards to build, I
don't think there's really a need to measure and QUANTIFY the actual height of
the solderpaste other than after initial set-up. I have never experienced the
height of printed solderpaste going up and down during a run once the printer
has been set-up (other than the tenths of a mil variations that you get
normally which has barely, if any, affect on the finished fillets) The way I
see it, especially with metal blades and the outstanding repeatability that
you get with most any printer nowdays, things won't change once the printer is
set. What measuring the print during a production run does in my opinion, is
to help ensure that at least somebody is periodically looking at the print
before putting all the parts on the board...and one can do that with a low
power magnification loop.

      So what do I use? Not a fancy-smancy, star-wars laser, $15,000
machine...(ain't got the moola for it for one thing), but a depth measuring
microscope that cost me a whopping $1,595...works the same way that a Vision
Engineering unit does if you've ever seen any of their stuff. It's good for
+/- .5-mil...same kind of accuracy the megabuck units have. I've always had a
hard time feeling comfortable with spending 15 grand just to measure
solderpaste. The unit I use is called a "SMarT Measure" and it's made by who
used to be known as Screen Manufacturing Technologies, but now is known as
Alpha Metals since they bought them out. If you're interested, call (408)
562-2033 and ask for Jim Vaughn. I bought the one I'm using here about
6-months ago (this is the third one I've bought for different companies that
I've worked for). It's a piece o' cake to use. Put the board beneath the scope
where you want to measure, focus on an exposed area of a pad, zero the digital
micrometer, then focus to the top of the printed paste and read the height in
tenths of a mil on the read out...what could be simpler? If you want, for an
extra $300 they also offer a little mini-printer that plugs into the
micrometer with a SPC program in it that will record your measurements and
plot them with the upper and lower control limits. Also, the microscopes
eyepiece comes with a measuring reticle graduated in mils so you can measure
X/Y too...(good to check pad dimensions on the board, aperture dimensions in
the stencil, measure leads or part dimensions for vision data for your pick an
place equipment, etc.)

      I'm not trying to slam the other pieces of measuring equipment on the
market, they're good too...but for $15,000 they'd better be! (if you catch my
drift)...

-Steve Gregory-

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