[SI-LIST] Re: Pick & Place Machines operation
- From: Erhan Kaya <Erhan.Kaya@xxxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 22 Oct 2002 12:20:36 -0400
Adeel,
When you say silk-screen this might mean the designators and other text,
figure etc printed on a board.
The board designer can include a layer in the design file for the HASL ("hot
air solder leveling" I guess) or whatever method will be used to cover the
copper pads. This definition for the pads will be used for stencil opening
file generation. I have never seen the design engineers suggesting an
"aperture" (stencil opening) shape/size to manufacturing. The process
engineer can directly send the pad definition to their stencil manufacturer
and ask them to do the "editing" per their previously sent document, or
define them in other ways. Sometimes asks for the rectangular shapes being
converted to triangles or just smaller rectangles etc.
Some process engineers might be picky enough to make their own change in
CAM350 etc, I don't know. But you can implement a better DFM methodology and
do the editing for them since you know a lot, or since they don't know much,
but they better learn how to edit these apertures since it's one of the most
important factors in getting a good solder joint.
It's difficult to give you an idea, really! After all calculations, the
manufacturer will come up with the number of hours spent. Then they might
multiply these hours with their labour rate. US$25 per hour per employee can
be a number for this. Some others know what it costs them to keep the line
idle for an hour from their overall annual costs. And some could be dying to
get more work and give a really good price. Hard to tell... If you give me a
component list or numbers I can try to get you a rough quote though.
Erhan
-----Original Message-----
From: Adeel Malik [mailto:adeelm@xxxxxxxxxxx]
Sent: Monday, October 21, 2002 7:42 AM
To: Erhan.Kaya@xxxxxxxxxx
Subject: RE: [SI-LIST] Re: Pick & Place Machines operation
Hi Erhan,
Thanks for the reply. Regarding the stencils, now I know their imp.
but can you further elaborate as to how they are produced and does the board
designer has to give a plot of Top Side Silk-Screen and Bottom Side
Silk-Screen of the PCB to the assembly for making a flaw-less stencil ?.
Secondly, regarding the cost, it appears to me that cost is proportional to
the variety of the components with different footprints as well as their
number. Can you give me a rough idea or guide me to a link having Assembly
rates for stuffing various SMD components in a given quantity?
Regards,
ADEEL MALIK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Erhan Kaya
Sent: Saturday, October 19, 2002 1:05 AM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: Pick & Place Machines operation
Adeel,
I am flattered with the over-estimation of my knowledge in that field. :-)
Anyway, I'll give it a shot but please remember, it's been 3 years since I
left that environment. Some of these things might not apply anymore.
1.
This is a 20 mil pitch. I remember seeing 14 mil wide pads for those parts
on the board and 6 mil spacing. Your 0.2 mm spacing between leads is 8 mils.
The leadframe must be a Jedec standard leadframe anyway, usually the process
guys don't care how close the leads are. Pitch is their middle name. And the
PCb designer has to give them a wider pad so that when the lead is soldered,
there are the toe, heel, and side fillets for a reliable solder joint.
Just tell them they're getting a 20 mil, QFP240 that's all.
2.
A machine has to know the x-y coordinates relative to an origin. Usually
there's a tooling hole at the bottom left of the board and that's (0.0). A
machine also needs to know the placement orientation. There are standard
orientations the parts are placed on tape as well as trays. And there's
always a first piece evaluation to see whether or not all the orientations
are correct. If there's a non-standard tape/tray or the CAD data is not
correct, it has to be modified during the trial run. Component designation
is also given, some machines use it some don't.
3.
Stencils are used at the Screen Printers where solder paste is applied to
the boards. Believe or not, the root cause for almost 80% of the process
issues are there. Usually it's a 6 mil thick stainless steel stencil with
very important apertures (holes) through which the solder paste is deposited
on the board pads. The paste is made from small tiny solder balls, with some
flux. If your 20 mil pitch part has 12 mil wide leads, the pads are usually
14 mil wide and the stencil opening is around 13. The paste deposited has to
be defined perfectly, so that the leads will sit on it nicely and the only
easy thing in process engineering: these leads will float and sometimes even
center themselves on that paste. If your board comes out of the PCB fab with
10 mil wide pads instead caused by excessive etching and the process guy
ordered his stencil opening 12-13 mil wide, then some of the paste will be
printed OFF the pad and there's no way those tiny solder balls will climb up
to the pad and join the rest to make a good joint. Result: Solder Balls -
the big nightmare
Just wanted to give one example to explain the importance of stencil design.
4.
This question needs a book. Starts from "quote generation" and ends with
"line optimization"
How much will I charge to populate your board? here's the formula I would
come up with:
- I would count the number of every different component type on the board
and find the tact time (placement time - i.e. 0.1 sec per part) and multiply
these two.
- Spread the placement among the parts you have on your line.
- Calculate the time your screen printer will use to print the paste on the
board.
- Find out the bottle neck on the line (where the board will spend the most
time)
- find the cycle time (one board comes out every x seconds)
- add your reel change, setup times, operator breaks etc and come up with a
number of hours per job figure.
- multiply with your hourly labour rate.
Then you optimize your line and try to reduce the cost.
- make sure the head speed on the chip shooters do not increase and decrease
from part type to part type. That is, since we're talking about a turret
carrying 10 - 20 parts at a time, to place one part at a lower speed,
everything else will be slow too. So, place the small tiny chips first and
then leave the larger parts to the end.
- watch the machine and find out what causes it waste time. Maybe the feeder
carriage moves back and forth too much, move feeders or change the feeders
to be picked up in a better order in the program.
- you can run the machine with a spare carriage setup and when there's a
part exhaust, the machine starts using the other carriage while the
operators take care of the part exhaust issue. The machine does not stop.
- implement offline setup so that the line will not stop while the next
job's feeders are being setup.
All of the above are process related. If you want to know what the design
guy can do to help, I can't think of anything really.
Sorry for the long email, let me know if there are any more specific
questions, or there's anything you think I misunderstood.
Erhan
-----Original Message-----
From: Adeel Malik [mailto:adeelm@xxxxxxxxxxx]
Sent: Friday, October 18, 2002 9:10 AM
To: 'Erhan Kaya'
Subject: RE: [SI-LIST] Pick & Place Machines operation
Helo Erhan,
Thanks for the reply. Some of the questions I needed to ask were:
1. How should one intruct the Assembly House about the positional accuracy
of the component. For example, if my design has a QFP package with the pitch
of 0.5mm and pin-to-pin spacing of 0.2mm (edge-to-edge), how it is
translated to the positional accuracy with which this QFP package should be
placed. ?
2. What are the necessary details one needs to give to the Assembly in the
Pick & Place Manufacturing File. This file generated by the PCB design
softwares usually contain the Reference Designators, the component's
centroid and its refernce position with respect to the origin. But is it
enough ?
3. What is meant by the Stencils and what is their significance in Automatic
Pick & Place operation ?
4. How the Assembly House evaluates the cost of Populating the components ?.
Can the board designer reduce the Polpulation Cost and if Yes, what are the
guidelines for efficient and cost-effective component placement ?.
Regards,
ADEEL MALIK
-----Original Message-----
From: Erhan Kaya [mailto:Erhan.Kaya@xxxxxxxxxx]
Sent: Thursday, October 17, 2002 11:23 PM
To: 'adeelm@xxxxxxxxxxx'
Subject: RE: [SI-LIST] Pick & Place Machines operation
Adeel,
If you have direct questions I can try to answer those. You might prefer
this to browsing newsgroups and going through deep discussions.
I used to place the components I design packages for now, and I might be
able to help.
Erhan
-----Original Message-----
From: Adeel Malik [mailto:adeelm@xxxxxxxxxxx]
Sent: Thursday, October 17, 2002 9:20 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Pick & Place Machines operation
Hi All,
I am sending some boards to the Assembly House for population and
for this I wanna acquaint myself with the operation of common Pick & Place
Machines such as how they pick the part from the reel, how they place the
component( with respect to the component's centroid or its reference
position....) and what type of Manufacturing file is required by the
assembly house.
Does someone know of the informative link providing basic as well as
advanced informaton about the Pick & Place Machines ?
Regards,
ADEEL MALIK
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