TECHNET Archives

August 1999

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Michael Fenner <[log in to unmask]>
Reply To:
Michael Fenner <[log in to unmask]>
Date:
Sun, 22 Aug 1999 13:54:58 +0100
Content-Type:
text/plain
Parts/Attachments:
text/plain (259 lines)
Hi Ingemar, sorry not to come back to you sooner, my PC is havng an identity crisis
leading to logging on difficulties. So this is Mike Fenner not Chris whatever the
headers footers might say.

To plod through the Q/A session below.
You are using prepacked dispense grade materials, so this eliminates any problems
arising out of mixing packing yourself.
I see you were using the PMF product from the freezer with only an hour delay, but
are now using it from the fridge, hopefully you are still waiting an hour and
hopefully this should solve a lot of your problems. Especially as your operator is
now aware that this is a crucial item and will be observing due procedure.

SOmewhere I have a an article on handling/using epoxies, I can send you this if you
like. Its not particularly high powered but most people have found it a useful
reminder. I can locate my original text and email it if you prefer. (I hope I can
find it as its a couple of years back by now)

On the airside of things, I appreciate that the idea of the auger systems is that
pressure is constant to avoid the sorts of things we are into now. BUT the adhesive
is still dispensed in discrete lumps under pressure, so somewhere in the system a
door is being opened and shut on a pressured column of material. There is a
difference I suppose betwen the door being opened/shut gently at the front of the
adhesive rather than being slammed around at the the back, but we are looking for
answers to an inexplicable problem so all things have to be considered to start with.

I think you will have some interesting times with using a Vshaped groove.  I didn't
see the postings to you suggesting this, but what is being described sounds like a
finest grind test. The problem is that the flakes will tend to be the same thickness,
but different diameters, when you wipe the blade across they will all lay flat and I
am not sure that you will find anything of interest. YOu might find that not all the
particles are flakes and you now get into an area of theology with adhesive suppliers
so I leave you to sort that out with them.
On looking at washed flakes I agree with I think PAul, its tough to do and anyway
what you are looking for is clumps which you will most likely wash away. Also of
course the flakes will crumple, so again I don't know what you will find. Basically I
think I would not spend too much time doing QA appraisals/vendor checks on materials.
If I had evidence of clumped (defective?) product I would ask my supplier to
investigate and show  his results...

So far as the suitability or otherwise of the Camalot system for adhesives vs solder
pastes and there being a better machine in Germany.  I was once told by a machine
vendor that most of the machines available - Camalot Assymptek etc all use the same
basic valves etc but they are just configered /utilised differently.
So I think you look at this in 2 parts. The first part you should check with Camalot
but I would be surprised. As to whether or not there is a better machine than Camalot
machine in Germany, given the German reputation for engineering I would not be
surprised, but I don't know.
It is quite conceivable that they have made a machine for Ag epoxies to take account
of the different morphology of the Ag filler, but I don't think this should be a
major issue. If you consider for a moment that graphite is an excellent lubricant....
This is because the plate shapes in graphite slide easily one over the other.........
Also recall that the flakes are made by flattening a sphere, so the thinnest
dimensions is very thin.
For these reasons I personally do not think the roughness inside the machine is too
important. Also I do not think 250 micron [0.010"] dots should be that hard to
dispense epoxy at. I think the problem is caused by the clumping of the epoxy and the
answer is to detemine when/how this occurs. Either it is before the material gets to
the machine = handling or they are being supplied.
And if there are no clumps going to the machine then the machine setup is causing it.
Then you need to plod through the various parts.

Hope this helps.



T: +44 1295 722 992
M: +44 789 999 7715
F: +44 1295 720 937


-----Original Message-----
From: [log in to unmask] <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 18 August 1999 15:06
Subject: Re: [TN] clogging dispensers


>Chris (Mike?)
>I have answered your questions below:
>
>--------------------Chris's mail----------------------------------
>
>Ingemar
>Some thoughts and ideas to consider/for discussion which address some of
>the items in
>your posting:
>
>First lets get the housekeeping out of the way:
>You don't say if you are buying one or two pack materials or premixed
>and frozen
>(PMF) etc.
>ANSWER:  PREMIXED AND FROZEN, 1CC TUBES BECAUSE OF EXTREMLY SMALL DOTS
>(DIA=300UM)
>
>Forgive me for asking but are you sure your people are properly
>observing storage and
>defrost requirements if PMF?  Commonly not enough time is allowed when
>taking
>material from the refrigerator or freezer. Another trick operators do is
>to warm the
>cold syringes in the hands to get them up to temp quickly. This can
>certainly give
>local curing in the syringe, especially if they return part used
>syringes to the
>fridge and repeat the hext day...
>ANSWER: OUT OF FREEZER, DIRECTLY IN MACHINE AMBIENT FOR 30 MIN
>UPWARMING, NO TRICKS. TODAY ABLESTIK TIPSED US TO MOVE THE CARTRIDGES
>FROM THE FREEZER TO REFRIGERATOR BEFORE ROOM STORAGE.
>
>Are you buying dispense grade materials prepacked by the supplier? Some
>suppliers do
>differentiate particle morpholgy/range and vehicle rheology
>characteristics for
>dispense and print grade applications.
>ANSWER: DISPENSE GRADE, ABLESTIK 8177
>
> IF you are repacking yourself then it is
>difficult to exclude air. Conversely if you are pulling a vacuum to
>de-air the
>adhesive then you are probably/possibly doing a better job than the
>original supplier
>would have done and this can have a big effect on rheology.
>ANSWER: REPACKING BY PUTTING  PACKAGE AGAINST CARTRIDGE. WE PRESS AIR
>INTO THE FIRST ONE WHILE SUCKING IN THE OTHER. DONT THINK AIR CAN COME
>IN.
>
>I do not see how humidity can influence dispense characterisistics as
>this would
>require the epoxy to react with airbourne vapour on contact . Even
>superglues which
>actually depend on humidity to cure can be dispensed. The only way I can
>see the
>epoxy dispense properties being effected by humidity is if you are using
>two part
>materials and mixing and packing yourself, but if you are in a clean
>room or
>controlled  environment then I would say your regular airconditioning is
>well
>overspecified to eliminate this effect
>So now all that is out of  the way....
>ANSWER: ONE OF OUR PHYSICISTS HAVE THE HUMIDITY THEORY IN MIND, BECAUSE
>SUCH THINGS HAVE OCCURRED, THE REST OF US DON'T BELIEVE IN THIS
>PHENOMENON AT THE MOMENT.
>
>Adhesives are much easier to dispense print than solder pastes, which is
>why such a
>lot is written about solderpastes and not much about adhesives. However
>much that is
>written about solder pastes doesn't really apply to adhesives as the
>particle size in
>adhesives is so much smaller, nevertheless it tends by its repetition to
>stay in
>one's mind. So for adhesives sudden dimensional changes roughness and so
>on in
>dispense paths do not have same significance as for solder pastes.
>
>Have you looked at your epoxy before and after dispensing to see if
>there is any
>difference in clumping?
>ANSWER: NO,  BUT WILL DO IT TOMORROW, BECAUSE YOU ARE RIGHT!
>
>
>If you reckon that a typical flake size for silver is around 5 microns
>max then you
>are seeing some agglomeration if you have 50 micron lumps. [You will
>most likely have
>a pointless time if you try to pin your supplier down in this area, but
>it sounds
>high to me]. If you are dealign with 50 microns this would equate to a
>preferred
>smallest dispense orifice of around say 250 microns and an absolute
>minimum of 150.
>If your mimimum IDs are less than say 3x -5x particle size then you will
>initially
>get dispense, but soon enough the particles will stack in the works
>somewhere. Then
>you will see a slow down in dispense rate, a little resin rich material
>being
>dispensed, and then blockage.
>This can be in as little as 2-3 minutes.
>ANSWER:  OK. WE HAVE ETCHED YOUR WARNING INTO EVERYONE'S MIND! BUT NOT
>ONLY THAT: WE WANT TO UNDERSTAND IN BASICAL TERMS EXACTLY WHAT HAPPENS,
>AND ALSO HOW TO AVOID SUCH DISASTER FOR EVER.
>
>If you are looking at high cycle rates you really do not want any air in
>the system.
>This could be in the back of the syringes/cartridges or even in the
>adhesive itself.
>Most concerns with air centre on its effect on accuracy of dispense,
>however air can
>produce effects you describe especially in in high cycle rate systems:
>If you have ever been in an old house or had problems with water heating
>systems then
>you will have heard the pipes hammering due to entrapped or generated
>gas. Something
>similar can happen in dispense systems with entrapped air.  If you have
>this effect
>then hammering or pulsing the epoxy can certainly cause flake separation
>/clumping
>and so on. I suppose it is possible that you could get local heating
>from this
>hammering effect but I don't see this being high probability.
>Normally in screw machines the air pressure is just to provide positive
>displacement.
>Maybe it  could be that you have a combination of high airpressures and
>too narrow
>dispense orifices. The high pressure being tried because of the dispense
>difficulties
>but actually aggraviting the problem.
>ANSWER: YES, I HAVE  HEARD GAS HAMMERING ON INSIDE (OF THE HOUSE).
>GOSTLY, INDEED! TO PROVE OR NOT TO PROVE IS THE QUESTION.
>
>MORE QUESTIONS:  ONE SENIOR TOLD US THAT CAMALOT'S SCREW PUMPS ARE
>DESIGNED FOR TIN/LEAD PASTES, AND ARE NOT SUITABLE FOR SILVER EPOXIES.
>IF YOU INSIST TO USE CAMALOT, THE SCREW SHOULD ROTATE AS LITTLE AS
>POSSIBLE, OTHERWISE THERE WILL BE FRICTIONING WHICH IN TURN WILL CAUSE
>HEAT, LOCAL CURING AND AGGLOMERATION. A GERMAN COMPANY IS SAID TO HAVE A
>PUMP, SPECIALLY MADE FOR SILVER EPOXY AND SMALL DOT CREATING.
>ANY COMMENTS FROM YOU MIKE?
>
>Regards / ???
>
>-----------------------end of Chris's mail----------------------------
>
>Are you Chris or Mike Fenner? I missed your signature.
>
>Anyway, many thanks for sharp comments
>Ingemar Hernefjord
>Ericsson Microwave Systems
>
>##############################################################
>TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
>##############################################################
>To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
>the body:
>To subscribe:   SUBSCRIBE TECHNET <your full name>
>To unsubscribe:   SIGNOFF TECHNET
>##############################################################
>Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
>information.
>If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
>847-509-9700 ext.5365
>##############################################################
>

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################

ATOM RSS1 RSS2