Karen,
I don't claim to be an expert in die attach, but ...
With devices this small it is always a challenge to automatically 'pick' them for a number of reasons.
Assuming the equipment properly 'sees' the chip and the pick-up tool is actually centered on the chip during pick-up [not necessarily a trivial endeavor] .... This can be a really simple oops, that makes for a difficult morning.
Also, the pick up tool is of a small OD - in this case 0.010-0.012" OD, therefore the ID is likely to be 0.006-0.008" ID [at most].
Small ID's generally do not have very much vacuum capability ... hence, the tool can not pull the small chip quite so vigorously. Sometimes special provisions like enhancing the bore of the tool, or generating a vacuum reserviour in/near the tool can help.
Although I can not say that I have physically proven this idea - Our machines pick with a much greater downward force than [I feel] is necessary. They are spring loaded. If I had a sticky spot underneath the device, and I pressed it down with a 50 gram force before subsequently attempting to pick it up from a waffle pack with vacuum, wouldn't the contact area of the sticky spot be greater [assuming that it had been squashed out somewhat] than if I were to pick it up with say a 20 gram contact force?? To me, the strength of a tape mastic is directly proportional to the coverage area ... So, small vacuum capability and the chip being 'extra-well attached' would mean poor pick consistency.....
We are picking off of membranes, so I can not provide a real 'hands-on' relative to picking from waffle packs - sorry. However, it is an idea that I happen to think deserves some consideration.
So, my foggy thoughts at this time of a foggy morning would be to minimize the contact force and maximize the vacuum capability of the pick-up tool.
FWIW
Steve
-----Original Message-----
From: [log in to unmask]
[mailto:[log in to unmask]]
Sent: Friday, August 27, 2004 2:41 PM
To: TechNet E-Mail Forum; Creswick, Steven
Cc: [log in to unmask]; [log in to unmask]
Subject: Re: [TN] Picking Die
Dear Technetters
Our die size is 0.012" x 0.012" x 0.006". Under 100x magnification we have
found tape residue on the back center of the die. As the Steve suggested
it appears that there is improper set up or needle selection going on. But
the other question nagging us is that we feel that this may have always
gone on. When we turn our die upside down in the waffle pack many of the
die stick. None of our other customer have an issue with this die and we
sell millions of these parts. We feel maybe something may be going on the
with the die attach process that something in the machine set up process is
not set quiet right. Any die attach experts out there with experience with
this problem that might help us identify how to eliminate this problem with
the pick and place process.
Thanks
(Embedded image moved to file: pic18467.pcx)
"Creswick,
Steven" To: [log in to unmask]
<SCreswick@GENTEX cc:
.COM> Subject: Re: [TN] Picking Die
Sent by: TechNet
<[log in to unmask]>
08/20/2004 07:57
AM
Please respond to
TechNet E-Mail
Forum; Please
respond to
"Creswick,
Steven"
Ingemar,
I am not totally sure that I understand your question, so if my response
does not adequately respond to your inquiry, please let us have another try
at it.
As I mentioned to Joyce, I would do this [destructive test] on a few chips
that had stuck in the waffle pack. My objective is simple - just like your
use of an eraser to investigate wire bonding surface characteristics - I
try to understand the source of the problem, so that I can reasonably
figure out what I may need to do to apply a remedy. I may not know exactly
WHAT it is, but knowing that SOMETHING is, or is not there, goes a long way
to understanding the problem [or re-directing the investigation].
My pseudo-analysis technique in this case would initially be VISUAL only.
I can see a great deal under an oblique light, with a low power microscope.
If I don't see anything, I switch to coaxial lighting, and/or greater
magnification. If I can not see anything in the range of 10X-200X with
oblique and coaxial illumination - it either isn't there, or it is SEM time
[or I have not yet had my spot o' tea].
Note: My pet peeve is when you give something to someone to look at, and
the first thing they do is put it under the microscope and crank the
magnification to maximum. As the old song goes, "they can't see the forest
for the trees". They have zoomed in so tightly that they have lost all
sense of the broader picture.
Anyway, I have a SiC chip. Being essentially transparent, if there is a
dot of mastic being transferred to the back of the chip during die attach
[just going directly from the membrane to the end product with no waffle
packs involved], it is really difficult to see the mastic on the back of
the chip [even when in the product, and silhouetted against the conductive
adhesive. However, if I cure the adhesive, THEN look through the chip I
will see a amber/brown spec if the mastic is present. Ditto, if I take the
chip and flip it belly-up [before sticking it down into the adhesive] and
simulate an adhesive cure.
Since some of my chips are still 'scored and broken', this can add another
variable to consider.
Now, with Si, or all the other opaque materials such as GaAs, AlInGaP,
InGaN, etc the illumination and angle of observation becomes critical.
There is no secret that I am aware of, other than trial and error.
Finally getting to what I believe is your question - would the mastic act
as an etch resist? Don't know, but is interesting thought. I wonder if
there is actually enough physical mastic present to act as an etch resist.
It would be interesting to try. I don't even know if we have HF acid here.
The chemistry folks have just about every other chemical under the sun, but
they are not to up to speed on semiconductor type stuff. I am not really
sure whether HF would etch some of the non-silicon based devices or not.
Maybe there is someone out there from an analysis lab that can chime in.
There is one other aspect from the original posting that we have not asked
yet - how large are the die that you are having problems sticking in the
waffle packs? Teeny tiny 0.008-0.012" diodes, or chips as large as your
thumbnail?
Granted, it does not take much to cause any device to stick in the cell
.... but small die probably stick more frequently than large ones :-)
If the ultimate cause of "device sticking in waffle pack cell" turns out to
be the mastic from the tape, then:
[1] Is it from the ejection needle? - mastic ideally in the center of the
chip. Indicating improper set-up or needle selection.
[2] Is it from something else in the pick process? - like the pick up tool
not being well centered about the ejection needle and maybe causing the
chip to slide slightly during pick-up (maybe picking up some mastic as it
moves)
[3] Is the face of the pick up tool orthogonal to the plane of the wafer
and fixturing? - if not, maybe the device slides again.
[4] Is it from the dicing/sawing operation? - mastic along the edge/s of
the device.
[5] Is it really new/old tape?
We have probably beat this to a pulp already with the various "what if's".
My general philosophy on this issue would be that unless the chips are
extremely expensive, or there are a really large number of them sticking in
the waffle pack - to just not use them!
If you have the time [or the need] to try to figure out the root cause fine
... maybe you can pass it along to an intern or something. I am sure that
we have all experienced missed-picks before. I just have not been pushed
to/over my threshold for action yet. That is not to say that someone else
has not, however.
Watch, the problem was likely found to be a dirty waffle
pack :-)
Hope that you are enjoying a nice weekend.
Steve Creswick - Gentex Corp
-----Original Message-----
From: Ingemar Hernefjord (KC/EMW)
[mailto:[log in to unmask]]
Sent: Friday, August 20, 2004 3:15 AM
To: [log in to unmask]
Subject: Re: [TN] Picking Die
Speaking dice,
you are two top experts on the stage, I take the opportunity to ask you
about this one: do you practice the analysis way by backetching the chips
and study them from 'underside'? What acidous process is best for GaAs
resp. Si?
Ingemar Hernefjord
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Creswick, Steven
Sent: den 19 augusti 2004 18:19
To: [log in to unmask]
Subject: Re: [TN] Picking Die
Joyce,
My suggestion for use of hotplate to determine presence/or not, of adhesive
was considered to be a destructive test. In no way would I do this as a
100% 'fix'
Any die tested in this manner would be considered as scrap
Steve
-----Original Message-----
From: Joyce Koo [mailto:[log in to unmask]]
Sent: Thursday, August 19, 2004 9:20 AM
To: TechNet E-Mail Forum; Creswick, Steven
Subject: RE: [TN] Picking Die
depend on type of chip... adhesive residue may cause high electrical
resistance if the back is used as ground. cook on the heat plate must be a
short time... otherwise, you may cause some degradation of wirebondability
(depend upon how clean is your hot plate... you can varify cleanliness of
your chip surface before and after hot plate using DI contact angle
measurement, you will see the difference)...If I were you, I'll check all
the vacuum pick, process parameter, etc. If everything is OK as per
qualification, you still got stuck die, I'll reject the lot for sure...(not
that make me popular...)
-my cold 1.52 cents..
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Creswick, Steven
Sent: Thursday, August 19, 2004 6:35 AM
To: [log in to unmask]
Subject: Re: [TN] Picking Die
Karen,
Bruce is correct in that the tape mastic should not be on the backside of
the device IF properly ejected, however, sometimes that is a big "if".
Many
individuals feel that you have to poke THROUGH the tape in order to eject
the device. I find that tends to transfer a small amount of adhesive, so I
elect NOT to poke through the tape. It is all a game of tip diameter,
needle travel, time, etc.
I have had similar experiences, but never to the magnitude that caused undo
grief. On occassion, I have washed waffle packs out with clean IPA and
this
has helped. For those [empty] waffle packs that seem prone to die sticking
[naturally, assuming the cavity size is large enough, etc], I just trash
them.
I have a few devices which are essentially optically clear. If there is
any
mastic transfer during the die ejection process, it shows up as a small
amber/brown dot after the die attach adhesive has been cured [can see it
from the top]. I guess from a silver lining stand-point this allows me to
verify just exactly where the ejection needle is contacting the device -
but
that is something I can generally do without :-)
I wonder .... if your device is large enough ... could you carefully remove
it from the waffle pack with tweezers, flip it upside down on a 200-250°C
heat stage for 10-15 minutes, char the mastic a bit [if it is there], then
pull it off and look at it under the microscope. I am guessing that if
mastic were there, it might show up if the lighting were just right.
I have had situations where the mastic is along the very edges of the
device. Believe this was due to cutting too far into the nitto tape during
dicing. Like Bruce said, this has been fixed with a better vacuum.
Just goes to show that even the little things are not so trivial.
Have a good day!
Steve Creswick - Gentex Corp
-----Original Message-----
From: Karen Walters [mailto:[log in to unmask]]
Sent: Wednesday, August 18, 2004 2:14 PM
To: [log in to unmask]
Subject: [TN] Picking Die
Has anyone ever experience die sticking to the waffle paks during die
attach. Please let me know what your solution was to this problem. We
believe it is Nitto tape residue that sticks to the back of the die when
the die are picked from the wafer ring to the waffle pak
Please let me know your experience with this.
(Embedded image moved to file: pic26500.pcx)
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