Author Topic: Pick&Place assembly line  (Read 12008 times)

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Offline Rundstedt

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Pick&Place assembly line
« on: July 11, 2012, 10:40:48 am »
Hello!
Menager of my company wants to buy pick&place assembly line (with reflow oven), I got a lot of info from Daves visit to ramzonics but I'd like to ask you for some advice:
-What machines look for?
-In ramzonics there was machine that applied solder paste through stencil, but I've seen cnc solder paste dispensers. From what kind of quantity it is more economical to use such machine?
-what parameters to look for?

 
 

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Re: Pick&Place assembly line
« Reply #1 on: July 11, 2012, 10:55:17 am »
Hello!
Menager of my company wants to buy pick&place assembly line (with reflow oven), I got a lot of info from Daves visit to ramzonics but I'd like to ask you for some advice:
-What machines look for?
-In ramzonics there was machine that applied solder paste through stencil, but I've seen cnc solder paste dispensers. From what kind of quantity it is more economical to use such machine?
-what parameters to look for?

I've also done a video showing a $26K solder paste CNC machine. They are only for prototyping or reworking, or maybe very small runs (like a few panels worth)

If your company is serious about this then you need to get in local dealer experts who can advise you based on your exact needs.
You don't set up a PnP line at a company on whim, and asking advice on forums :->

Dave.
 

Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #2 on: July 11, 2012, 05:18:40 pm »

If your company is serious about this then you need to get in local dealer experts who can advise you based on your exact needs.
You don't set up a PnP line at a company on whim, and asking advice on forums :->

Dave.
Wow, I got response from Dave himself!

But unfortunately you never worked at my company. I just ended 2nd year at university I had no prior experience in commercial work and yet I basically have to create a whole R&D. I have huge responsibility whilst earning less than cashier (but I'm still very grateful for it, and I love it so much)

Manager decided that we will buy used PnP assembly line we will learn to use it and then know what to buy next. With production of some components from very small quantities (setting this machine will take probably more time than hand soldering) to thousands of sensors (still I think more economical would be to just pay some manufacturer to assemble it). That's why I decided to ask on forum what to look for, you say ask local dealer. Maybe it works better in Australia but from my experience if you want to buy something you know completely nothing about you they will take advantage of that.
I know some things already (mainly from your videos) like how many components can machine grab each time, how small components it can pick, can it pick from trays. I know next to nothing about what reflow oven to look for.

I won't base my opinion only on forum posts, I will look on other sites and sources.

I don't want to make impression that I want you to do my job for me. I'm just confused young man with huge tasks ahead, trying to learn as much as I can in shortest time possible.

 

Offline EEMarc

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Re: Pick&Place assembly line
« Reply #3 on: July 11, 2012, 11:12:10 pm »
Are you working for a startup?
 

Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #4 on: July 12, 2012, 01:59:02 pm »
Are you working for a startup?
no, they are on market more than 10 years
 

Offline mikeselectricstuff

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Re: Pick&Place assembly line
« Reply #5 on: July 12, 2012, 02:13:50 pm »
This forum may be of some help, as it's fairly industry-based
www.smtnet.com/Forums/

As a minimum you will need :
A paste stencil printer - a manual one may do initially - I know some fairly big assemblers that still do manual printing. Even a manual one does need to be something well made and very solid for accuracy, with good adjustability, as paste print quality is about the most important factor in getting good results.
Expect to pay $1500-5000 for used or low-end new.

You also need a reflow oven. For small volumes a toaster oven (with someone watching it) is useable but you will probably want a conveyor oven at some point.

As for the P&P machine itself you can spend $5k to $5m , depending on what you need. there are bargains in used old machines but they may need siginificant time to getr running well.  Don't forget to allow for the cost of feeders - on used machines these can often add up to more then the machine as used feeders are in more demand than used machines.
You need to look carefully at your batch sizes, typical component mix, max number of different parts (=how many feeders you need) etc. Placement rate is probably a secondary consideration, unless you have high enough component counts to keep the machine busy most of the time.
Placement rates start at around 1500 components per hour. Note that manufacturers often exaggerate cph figures, like printer makers exaggerate ppm. e.g. they may quote for placing parts from the nearest feeder to the nearest edge of the PCB.

Some machines also need a compressed air supply, and you may also need fume extraction for reflow. Reflow ovens often need 3-phase power.
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Offline Psi

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Re: Pick&Place assembly line
« Reply #6 on: July 12, 2012, 02:26:47 pm »
But unfortunately you never worked at my company. I just ended 2nd year at university I had no prior experience in commercial work and yet I basically have to create a whole R&D. I have huge responsibility whilst earning less than cashier (but I'm still very grateful for it, and I love it so much)

Your job sounds both scary and very exciting. However i dunno if i'd want to do it while earning less than a cashier.

I think here most cashiers get minimum wage, so less than that wouldn't be possible :P
« Last Edit: July 12, 2012, 02:33:25 pm by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #7 on: July 12, 2012, 02:53:14 pm »
But unfortunately you never worked at my company. I just ended 2nd year at university I had no prior experience in commercial work and yet I basically have to create a whole R&D. I have huge responsibility whilst earning less than cashier (but I'm still very grateful for it, and I love it so much)

Your job sounds both scary and very exciting. However i dunno if i'd want to do it while earning less than a cashier.

I think here most cashiers get minimum wage, so less than that wouldn't be possible :P
Well minimum wage in Poland is 320 USD after taxes, I earn 460. Working 30km from capital. And to be fair it is while I'm on 3 months trail, after that period I will renegotiate my wage. And even though I seriously love work in development, this is too much responsibility for that kind of money.
 

Offline mikeselectricstuff

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Re: Pick&Place assembly line
« Reply #8 on: July 12, 2012, 04:50:54 pm »
Quote
after that period I will renegotiate my wage.
Well if you set up a production line and are the only one who knows how to use it, it puts you in a good negotiating position... 8)
Have they given you a target budget?
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Offline Psi

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Re: Pick&Place assembly line
« Reply #9 on: July 13, 2012, 01:12:04 am »
haha yeah, he raises a good point.


Also, you can add   "Setup a full pick & place / reflow assembly line"   to your CV, which sounds awesome :D
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline EEMarc

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Re: Pick&Place assembly line
« Reply #10 on: July 13, 2012, 03:33:59 pm »
In that case, I can see why you are working hard while starving. The thing that a startup would answer that I still haven't figured out is why would a company that has been in business for over a decade not have experience in making boards, a key component. I can come up with two guesses outside of a startup. One is a switch from through hole to surface mount. The other is a new set of products that use electronics to the extent of requiring PCBs where the old products did not.

For very low volume, it is often better to do it by hand. Like you mentioned, the setup time both initial to teach the machine how to operate, and to switch to that job in the future are quite time consuming. Add in the stencil cost, the time it takes to setup the reflow oven and stencils, and the fact that the machine will make most of it's mistakes on the first few boards/panels made results in additional cost in labor, parts, and expense. In this case, focus on getting good equipment for hand soldering SMD. This equipment will be good for low volumes stuff and also the inevitable rework for higher volume stuff. The keys to good hand soldering is very good lighting. Good magnification for fine pitch stuff. Good soldering equipment. High quality component handling equipment such as tweezers, vacuum pick up tools. Foot pedal operated paste dispenser. In many cases, I can place just as fast as a low end machine with the right setup. I just don't like to do this for extended periods of time which is why I use a PnP machine. When you are done, stick it in the reflow oven and let it work it's magic. You can get away with a less than good setup for a few boards, but when it comes to working a full shift soldering, you really need a good setup. Especially very bright lighting and good optics to relieve eye strain.

If a low volume product picks up in sales, upgrade it to PnP status. Just make sure that all of the designs are PnP friendly for best results. Some PnP machines have the ability to attach a syringe with attached pneumatic solenoid to apply it to the board. You can put paste or glue down where you want it. For the low volume example, you can get away with not getting a stencil for a given board by having the PnP machine paste the pads before placing the parts albeit, you are taking away machine time so a stencil is often a good investment. Better use is for the ability to paste is a new revision with the addition of an extra cap  or two or something else simple where other parts aren't moved. The stencil doesn't place paste where is doesn't belong, so fill in the new parts and save the cost for a new stencil. Alternatively, you can use glue to hold parts down. This is the secret for making 2 side component boards where you place parts on one side and run it through the oven. The second run through, the upside down components will be firmly attached except during the reflow portion. This also plays a roll in the choice of reflow oven. If you have a type of oven that will touch the bottom of the board, you will need to make a frame block for the boards/panels to lift them up. Small parts such as ICs and resistors, small caps, will be held in place by the solder's surface tension. The large components will fall off so glue them in place. If a part falls off, use your rework station to fix it and add glue next time. It will take some effort to get 2 side component boards to run well, but it is well worth the effort.

When it comes to pick and place, feeders are very important. Both in how many you get and how many places the machine can hold. You can have 10 different products or more that can run with 1 setup because they use a large number of the same components. Simply formulate a setup plan with all of the products and feeder locations. Simply load the the feeder plan, load product A's PnP file, put the stencil in and set the paster up, and set the reflow oven up. Then run the product A board through. When done, change the paster for product B, Change the PnP program, Change the reflow oven if needed, and run product B. Then C. And so on. If you have boards with similar reflow oven profiles, same it's setup time by running them back to back. This is the kind of thing you can do if you have enough feeders and enough feeder slots. If you run out of feeder slots but have enough feeders, set the later feeders up and simply swap a few feeders out when you need to.

If machine time is a limiting factor you can optimize the placement rate by selecting prime feeder locations for the most popular components such as 0.1uF capacitors and certain resistor values. Usually the closes feeder slots to the actual board are prime feeder slots. The time it takes to move to a feeder location, pick the part up, move to the board, and place can be very different for each feeder slot. Far away feeders take much longer than feeders right next to the board. For long runs especially, it can save a lot of time to move popular parts to prime locations. Notice in the uCurrent video that the locations selected are very close to the board allowing placement rates of roughly 6 parts per second. The optimization is also important for where to place the feeders relative to each other. Notice that the simultaneous pickup picks from specific reels. If not optimized, the head will have to move between picking up the parts slowing down the action. Low end machine often will not have simultaneous pickups but there is still gains to be made from relative feeder locations. There are also machine specific optimizations to be made.

For larger components that need to use the bottom vision as opposed to on the fly vision, remember that the next place after going to the feeder is to the bottom vision camera. This means that the prime location for bottom vision components is different than vision on the fly components. Also notice that the uCurrent video, the machine only uses 2 heads and the placement rate is very slow compared to on the fly vision placements. A tiny fraction in fact.

As for hookups, you need the right hookups. If you have single phase service only, try your best to get single phase machines. It is expensive to get a single to 3 phase converter or have 3 phase service put in. You may need to have dedicated circuits and special high current outlets installed depending on the reflow oven in particular. Nothing will ruin your day more than having the circuit breakers pop. 

If your machine needs air, either tap into shop air or you will need a good heavy duty oil filled compressor sized for your needs. If you have shop air service, you need to make sure that there is enough excess capacity to handle your machine. Venturi effect created vacuum uses a large volume of air. Keep that in mind. I prefer to use a good quality vacuum pump as it is more efficient than using shop air. Even if the machine doesn't use it, shop air is still very useful. Also, once shop air is available, others will probably want to put there stuff on it.  Make sure that you have some capacity for them if this will happen and also make sure that they don't cause problems by using too much air. This is especially a problem with some blower attachments that use a ton of air. If you do install some shop air, make sure to control condensed water. Usually the level plumbing will be at a slight slope to allow the water to flow. The best options is to have it flow back towards the compressor to a drop down line with the incoming air in a T. This is where the excess water is allowed to drain down to a stub pipe that collects water. Put a valve there to drain the water out of the line. For drop downs to machines and other workstations, the best practice is to use and upside down U pipe going up then back down. This will prevent the T from dumping water into the machine. It is good practice to also have a drain at the bottom of the drop down as well to collect and release any water that does condense there. With shop air, I'm considering adding a refrigeration unit to the shop air outlet. This is called a drier and it will eliminate all water from condensing in the system beyond the drier. The drier will need to be drained of condensed water.

Machine placement is also important. You don't necessarily need to have an assembly line setup. With low end machines, it is a good idea to inspect the boards after placement to fix the mistakes before putting the board through the oven. This can save time over reworking a board later. As for ideas for setting up a line, there are many good youtube videos that show some interesting setups. You can pick up some very useful hints and techniques from many unlikely sources. My favorite on there that I have seen is the Apple Macintosh Fremont California factory. I know a couple people that worked on the original Macintosh. It's funny to see Macintosh computers make more Macintosh computers.
 

Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #11 on: July 13, 2012, 09:05:25 pm »
haha yeah, he raises a good point.

Also, you can add   "Setup a full pick & place / reflow assembly line"   to your CV, which sounds awesome :D
Well that would be awesome indeed.
In that case, I can see why you are working hard while starving. The thing that a startup would answer that I still haven't figured out is why would a company that has been in business for over a decade not have experience in making boards, a key component. I can come up with two guesses outside of a startup. One is a switch from through hole to surface mount. The other is a new set of products that use electronics to the extent of requiring PCBs where the old products did not.
Well while they were on market, their electronic stuff was (and still is) produced by outside companies, they look into integrating everything into company that's why I'm in charge of developing electronic products, and finding machines to buy.
For very low volume, it is often better to do it by hand.
Well it would be far too much to produce by hand, even now. At least 3000 MAP sensors a year. And a few other products.
When it comes to pick and place, feeders are very important. Both in how many you get and how many places the machine can hold. You can have 10 different products or more that can run with 1 setup because they use a large number of the same components. Simply formulate a setup plan with all of the products and feeder locations. Simply load the the feeder plan, load product A's PnP file, put the stencil in and set the paster up, and set the reflow oven up. Then run the product A board through. When done, change the paster for product B, Change the PnP program, Change the reflow oven if needed, and run product B. Then C. And so on. If you have boards with similar reflow oven profiles, same it's setup time by running them back to back. This is the kind of thing you can do if you have enough feeders and enough feeder slots. If you run out of feeder slots but have enough feeders, set the later feeders up and simply swap a few feeders out when you need to.
Good tip, but probably most of them will share few resistors and capacitors
If machine time is a limiting factor you can optimize the placement rate by selecting prime feeder locations for the most popular components such as 0.1uF capacitors and certain resistor values. Usually the closes feeder slots to the actual board are prime feeder slots.
I do not think that time will be a factor now, but tis is another great tip to consider.
As for hookups, you need the right hookups. If you have single phase service only, try your best to get single phase machines. It is expensive to get a single to 3 phase converter or have 3 phase service put in. You may need to have dedicated circuits and special high current outlets installed depending on the reflow oven in particular. Nothing will ruin your day more than having the circuit breakers pop. 
No, that's not a problem. We have our own transformer, compressed air or fume extraction also isn't a problem.
Quote
after that period I will renegotiate my wage.
Have they given you a target budget?
No they haven't cause they don't know how much they have to spend (yeah, I see the irony). They now want to buy used line to see in production what we need, and then buy new one. But I'm trying to force buying new one, with EU help we would probably pay half or even less but to get EU help we need to write proposal for specific machines. And usually when someone sells that kind of line there is a reason to sell it (I figured), either mechanics are getting screwed up or it can't pick up some elements.
Now I look though some responses from dealers to get orientation in prices.

Thank you all for the tips, if you have others, please share.
 

Offline poorchava

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Re: Pick&Place assembly line
« Reply #12 on: July 14, 2012, 09:06:22 pm »
Heh, what company do you work for? I'm just curious.

Btw. If you feel like you're nor earning much, then maybe you can look for some company with foreign captital. Dunno how in your location, but here in Wroclaw (and nearby) we have quite many companies from electronics & IT market: Nokia Siemens, IBM, Espotel, Diehl Electronics, WABCO, TechniSat and others. And usually starters net salary for person with masters degree in whatever engineering type is around $800-900 (base is around 1100 but taxes and worthless social security take like 1/4...1/3).

On the other hand it's quite nice ocasion to put yourself in a position, where your employer can't afford to fire you :)
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Online IanB

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Re: Pick&Place assembly line
« Reply #13 on: July 14, 2012, 10:56:26 pm »
Well while they were on market, their electronic stuff was (and still is) produced by outside companies, they look into integrating everything into company that's why I'm in charge of developing electronic products, and finding machines to buy.

Bringing manufacturing in house seems like an odd step to be taking. Usually the companies you would contract out to would have at their disposal much more sophisticated machines with greater capabilities due to the volume of work they undertake. Since they would be specializing in manufacture you would expect them to be more efficient and more consistent too.

What is driving the in-sourcing of the work? Is it to have greater flexibility and control with faster turnaround times perhaps? Or are there quality problems with the outside contractors?

I have no great knowledge of this, but I'm curious. One normally would expect to concentrate on the part where you have most value to add (product design and customer satisfaction) and to delegate the routine aspects like circuit board assembly to other companies that specialize in that area.
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Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #14 on: July 15, 2012, 09:15:00 pm »
Heh, what company do you work for? I'm just curious.

Btw. If you feel like you're nor earning much, then maybe you can look for some company with foreign captital. Dunno how in your location, but here in Wroclaw (and nearby) we have quite many companies from electronics & IT market: Nokia Siemens, IBM, Espotel, Diehl Electronics, WABCO, TechniSat and others. And usually starters net salary for person with masters degree in whatever engineering type is around $800-900 (base is around 1100 but taxes and worthless social security take like 1/4...1/3).

On the other hand it's quite nice ocasion to put yourself in a position, where your employer can't afford to fire you :)
I don't even have engineering degree yet
Bringing manufacturing in house seems like an odd step to be taking. Usually the companies you would contract out to would have at their disposal much more sophisticated machines with greater capabilities due to the volume of work they undertake. Since they would be specializing in manufacture you would expect them to be more efficient and more consistent too.

What is driving the in-sourcing of the work? Is it to have greater flexibility and control with faster turnaround times perhaps? Or are there quality problems with the outside contractors?

I have no great knowledge of this, but I'm curious. One normally would expect to concentrate on the part where you have most value to add (product design and customer satisfaction) and to delegate the routine aspects like circuit board assembly to other companies that specialize in that area.
Well there are many factors:
- there are little to no after-warranty services. Since we didn't design product there isn't a lot what we can do to repair it.
- there are some little difficulties with our contractors (some minor errors in product that they refuse to acknowledge)
- we export a lot to China/India/Thailand and other cost sensitive markets, and producing in-house will cut expenses (you say that outside companies have better machines, but we are looking at similar line)
- we have no control over producing capabilities of companies we hire, sometimes when they have too much other orders they will put ours at back burner.

There are a few other reasons to.



 

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Re: Pick&Place assembly line
« Reply #15 on: July 15, 2012, 10:39:50 pm »
Well there are many factors:
- there are little to no after-warranty services. Since we didn't design product there isn't a lot what we can do to repair it.
- there are some little difficulties with our contractors (some minor errors in product that they refuse to acknowledge)
- we export a lot to China/India/Thailand and other cost sensitive markets, and producing in-house will cut expenses (you say that outside companies have better machines, but we are looking at similar line)
- we have no control over producing capabilities of companies we hire, sometimes when they have too much other orders they will put ours at back burner.
There are a few other reasons to.

Fair enough of course.
Have you actually been tasked with looking into this?
Your manager needs to be made aware that this is a big, expensive, and complex undertaking that will take a lot of work, time and support to get running smoothly. You can't just buy the machines and expect magic to happen  ;D

Dave.
 

Online IanB

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Re: Pick&Place assembly line
« Reply #16 on: July 15, 2012, 11:40:09 pm »
Well there are many factors:
- there are little to no after-warranty services. Since we didn't design product there isn't a lot what we can do to repair it.
- there are some little difficulties with our contractors (some minor errors in product that they refuse to acknowledge)
- we export a lot to China/India/Thailand and other cost sensitive markets, and producing in-house will cut expenses (you say that outside companies have better machines, but we are looking at similar line)
- we have no control over producing capabilities of companies we hire, sometimes when they have too much other orders they will put ours at back burner.

There are a few other reasons to.

It seems a little odd to me that if your company didn't design the product and doesn't make the product, what does your company actually do? What is the value add?
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Offline Rundstedt

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Re: Pick&Place assembly line
« Reply #17 on: July 16, 2012, 08:56:17 am »
Fair enough of course.
Have you actually been tasked with looking into this?
Your manager needs to be made aware that this is a big, expensive, and complex undertaking that will take a lot of work, time and support to get running smoothly. You can't just buy the machines and expect magic to happen  ;D
Dave.
Yep, but when I learn to operate such line it will be just awesome.

It seems a little odd to me that if your company didn't design the product and doesn't make the product, what does your company actually do? What is the value add?
Well they started from trading parts, later they started to order custom parts for them and "making" complete kits for lpg/cng conversion. We assemble some parts, but mostly we are just the middleman.

Actually I grossly underestimated how much production capabilities we need, we need about 100k small boards 40x60 mm with about 10 different parts, 100k 120x70 mm with 40 different components and another 100k of 25x25 mm boards with 15 components (both sides). And a few thousands of other boards. Currently some company offered us ax-501 (used 10 months). Can anyone suggest me how many zones will I need in reflow oven, and do we need to solder in protection of nitrogen (led free solder of course), what types of transport for pcb there are?. Should paste dispenser be vacuum cleaned or wet cleaned.

Sorry for all those questions, Jarek.
 

Offline mikeselectricstuff

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Re: Pick&Place assembly line
« Reply #18 on: July 16, 2012, 10:40:21 am »
Fair enough of course.
Have you actually been tasked with looking into this?
Your manager needs to be made aware that this is a big, expensive, and complex undertaking that will take a lot of work, time and support to get running smoothly. You can't just buy the machines and expect magic to happen  ;D
Dave.
Yep, but when I learn to operate such line it will be just awesome.

It seems a little odd to me that if your company didn't design the product and doesn't make the product, what does your company actually do? What is the value add?
Well they started from trading parts, later they started to order custom parts for them and "making" complete kits for lpg/cng conversion. We assemble some parts, but mostly we are just the middleman.

Actually I grossly underestimated how much production capabilities we need, we need about 100k small boards 40x60 mm with about 10 different parts, 100k 120x70 mm with 40 different components and another 100k of 25x25 mm boards with 15 components (both sides). And a few thousands of other boards. Currently some company offered us ax-501 (used 10 months). Can anyone suggest me how many zones will I need in reflow oven, and do we need to solder in protection of nitrogen (led free solder of course), what types of transport for pcb there are?. Should paste dispenser be vacuum cleaned or wet cleaned.

Sorry for all those questions, Jarek.

If you are talking these volumes (I assume annual) you need to pay an expert to advise you, as you will be spending well into six digits on setting up a line for this capability, and mistakes can be very expensive.  You will need to employ several full-time staff to run the assembly line, manage inventory, handle QC and test.

This would be a massive investment -  it sounds to me like both you and your management are hopelessly out of your depth.

For these volumes, outsourcing to a Far East assembly house would seem to be the obvious solution.
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Offline EEMarc

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Re: Pick&Place assembly line
« Reply #19 on: July 16, 2012, 08:13:11 pm »
Actually I grossly underestimated how much production capabilities we need, we need about 100k small boards 40x60 mm with about 10 different parts, 100k 120x70 mm with 40 different components and another 100k of 25x25 mm boards with 15 components (both sides). And a few thousands of other boards. Currently some company offered us ax-501 (used 10 months). Can anyone suggest me how many zones will I need in reflow oven, and do we need to solder in protection of nitrogen (led free solder of course), what types of transport for pcb there are?. Should paste dispenser be vacuum cleaned or wet cleaned.

Sorry for all those questions, Jarek.

That is a cool PnP machine. Parallel placement means substantial throughput. This means that you can still have a substantial amount of downtime and catch back up with ease. Also, having spare capacity gives opportunity for getting outside contracts to have boards built on your assembly line. This will help offset the amortization of the machine's cost to your favor and provide a potentially valuable revenue stream for your company. In other words, outside contracts could potentially pay for the machine and then some. Running your own boards will then be reduced to the simple cost of labor and utilities. This will also help make the cost benefit analysis look more appealing. Just don't forget about gluing larger parts down for 2 side component applications.

The paster, stencil cleaner, reflow oven, and use of nitrogen are all interrelated issues. Changing one will likely change the choice of others. It's hard to make recommendations here without a full knowledge of the product running through the machine. Nitrogen will get better RoHS solder wettability and solder joint quality as well as have a higher surface tension which is useful for holding upsidedown parts through the reflow. It also will screw with the reflow oven's temperatures, and have higher quality requirements for paste application and stencil cleaning.  The goal is to not need to use nitrogen since it is an additional expense. Selection of a good solder paste may or may not negate the need for it. You will also want more zones particularly for just after reflow to prevent popcorning/tombstoning of the components as they go through the temperature cooling. You'll see this when one side cools faster than the other side, usually during too fast of a cooling rate before solder solidification. If the leads are at too much of a different temperature, the torque caused by the cooling and contraction of the solder will cause it to lift the opposite end of the part off of the board. This is common with hand soldering surface mount components if you don't hold the part down. It is particularly bad with tiny components.

RoHS is slow to wet out without nitrogen and you wil need to take care else you willl have some thermal issues with nitrogen. Also, look at how much your components size vary. If you are combining small resistors and capacitors with DPAK, D2PAK, or IC's with thermal pads soldered to the board or have multilayered boards, you will want more zones. Each device has an acceptable thermal profile for reflow. you will need to find a line that is acceptable for all components used on a given board. The more zones you have, the easier it is to get a good reflow for all components, tiny and heavy. Going outside of the envelop will increase the failure rate.  Also, remember that each part and pad has a thermal capacity, small parts will heat up quickly while heavy parts will take longer. One problem that you may run into is heating up enough to solder heavy components while not cracking Multi-Layers Ceramic Capacitors (MLCC) for example. Having more zones available will help you optimize the machine so that you can heatsoak the board enough to allow the heavy parts to reflow properly and keep the ceramic caps safe. Nitrogen will help with this.

In general, more zones will give you better control. Keep in mind that not all zones are made alike. A cheap machine could have 50 zones yet do a terrible job because of thermal shock. The key to reflow is controlling and limiting the rate of change of the temperature to precisely match predetermined temperature profile. A good machine will be able to do this with minimal zones in some cases, but more zones does help especially with more demanding requirements. If not careful with nitrogen, you can cause thermal shock regardless of how many zones you have. In general, if you get the minimum number of zones that you need, you'll always end up wanting another one to help tweak the machine's operation.

To determine the precise setup, you will want the advice from someone that has setup a number of successful RoHS PnP lines and has full knowledge of your application. They will be able to help you hone the fine details out for the equipment that you need. Always seek unbiased advice from someone that isn't getting a sales commission. This conflict of interest won't work to your company's benefit even though it may seem cheaper upfront.

-Marc
 


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