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May 21, 2019 | Step-up stencil: recommendation thickness Thanks to @davef and @Evtimov for trying to help. It's useful but not exactly the answers I would like to get. I'm going to reformulate my question. I'm writing in mm so that it's more precise: I have a 0.12mm-thick stencil for some 0.4mm-pitch QFN. There is a big BGA 1.13mm-pitch module that has a tendency to wrap or to be at angle which creates open pads. I would like to have a step-up stencil at 0.15mm or 0.16mm below the module. My concern is the risk of shorts because of the added solder. At what thickness should I be worried for 1.13mm-pitch pads?
Apr 9, 2018 | Nordic aQFN73 stencil design under them and we did the typical 4X windowpane layout for the 4 mil stencil that we would normally use for anything like this. They skewed badly. The manufacturer's recommendation for the paste file is a solid square aperture, just like the customer provided. That goes against everything I know have your stencil cut for them? Thanks!
Dec 1, 2017 | I am not sure that is doable. Ground Aperture is very small(for the stencil blade to get in there) and very close to the other apertures. I want to say the minimum requirement for step is 6mm clearance from other apertures for the stencil houses that I worked with. There might be a requirement for minimal size of the step as well. You can always ask your stencil house, but I can't foresee a visible effect doing that. Most likely is to stick these paste into the holes given and see what you end up with as coverage under the part on the X-ray. Another solutions will be PCB design related. I would ask
Nov 15, 2017 | IMO – Look into nano-coatings for your stencil and radius all square apertures This should help out with solder paste releasing from the stencil helping with insufficient solder QFN LGA aperture design, try a stencil cut with a few different aperture designs to test. I have had success
Aug 13, 2017 | into > delayed delivery shipment, cost increases, and > considerable (but unnecessary) stress being > placed on the board's existing components. This flaw could be due to inaccurate stencil design, among other factors. The assembly process can incur adverse effects when the stencil is not accurately designed. There can be such flaws as a number of tombstones and bridging when an incorrect stencil is run through the pick-and-place and reflow process.you share the screenshots of GTL with GTO and GBL with GBO for a further check?
Apr 18, 2017 | Dear PCBFOX, I use CAM350 v12.2 build 1135. I am trying to use CAM350 DFMStream module for paste mask layer check. Examination I am interested in most of all is "Paste Mask Layer Check - Missing Paste Mask on SMD Pads (MP)", i.e. missing stencil apertures. In order to run this check I do next : - import GERBER and drills - setup layer types in the layer table - add and setup DFMStream - intentionally delete one stencil aperture in order to see how examination works - run DFMStream Having intentionally deleted an aperture, the problem is that DFMStream finds zero errors. Important points is that there are no components in the design. If I manually define components than MP check will work. What am I doing wrong? Is it possible to find missing stencil apertures for GERBER data only not having defined any components in the design. Any input would be really appreciated. Regards, Pavel
Mar 10, 2017 | Stencil Manufacturer What part of the country are you located? I know numerous stencil manufacturers in the country that I could refer you to. The one we currently use is Stentech and guarantee next day delivery for basic laser cut stencils. They have always kept their word on this and I have been using them for 7years
Jan 27, 2016 | You can buy an awful lot of stencils for $200K but where/how are you going to store all of those stencils? There is a certain $$$ value to all the space it will take to store them. I have been told by a Mycronic salesman that they are working on qualifying water soluble paste for the MY600 . However, it has been almost a year since I was told that and they still have not come out with it. We do not have a jet printer but there are times when I wish we did. We buy around 25 stencils every year and I am starting to run out of space to store them. Our volume/revenue is not high enough
Sep 16, 2015 | Cleaning a Used (Preowned) Selective Solder Machine Problem with cleaning these machines is once you start it's easy to get carried away. ;) We cleaned our SPA-400F a few months ago, had been offline for a while as we were using our SPA-250. It started as just a clean and to replace all the flux pipes etc. We ended up fully stripping the machine as the solder can spit out. It's useful to turn the heater off every 15 mins for a bit to prevent this. 5. Fluxer is key as has been said. We always clean the fluxer at the end of every day and do this throughout the day depending on load.
May 13, 2013 | is actually a special feeder and it is 15K USD. We don't have enough assemblies to make this purchase reasonable and that's why I keep cutting stencils. However, for one job we had to cut3 Nickel stencils before we get it to work properly.If you have to cut 20 stencils(Ni or e-formed) this year you should
Jan 12, 2013 | . The machine should have come with a large copper clad board (20"x20", or 508x508mm) and a stencil with a LOT of circular aperatures in a grid across the entire printable area. The jist of this is that you would print the grid onto the copper plate and then the camera would inspect the offset between the stencil "hole" and the paste deposit. It's almost the same idea as mapping a PnP machine. This is much different than older MPM's where offsets could be performed in minutes. Perhaps you could contact the seller of the machine to see if they have it. Quite often it gets mixed in with their stencil
Jun 29, 2012 | on the next one at the same PCB. I'm guessing that maybe the stencil has some offset or maybe the board, we are getting many bridging errors, I have tried 2 stencils but same results, is it common to have offsets from the stencil or PCB manufacturer for this uncommon size? I'm using a carrier to hold PCB
May 27, 2012 | I'm with SWAG. Print a 1:1 transparency of your stencil file and mark it where you want to place the pins. Place it in the product file and use it each time yor run that product. 1. Get the pcb into the print position. 2. Tape your transparency to the conveyor rails so it matches the pcb. 3 . Remove the pcb 4. Place the pins under the transparency. 5. Remove the transparency and run. As far as rev changes to the pcb go - if you have to fab a new stencil - print a new transparency, it'll cost you all of 50 cents. I won't have a stencil made in the first place until I've matched the pcb to it
Mar 22, 2011 | Stencil Inspection At times, yes. We do high volume, fine pitch on flex panels and if we need a 8 mil width aperture, it can't be 9 or 7. It has to be 8 and we have seen times where the tolerance is +/- 1 mil. Additionally, we have received stencils with abnormally rough sidewalls. I don't know what the tolerance the need for tighter stencil control.
Jan 13, 2011 | Cleaning a No Clean Not sure this would be of some help, but in the past I worked in the OEM industry in a fully No Clean process using A*M NC Solder. If customer expectations cannot be tempered, you're stuck cleaning the No Clean. To remove the NC residue, (which we did for no other reason than our customers wanted
Aug 30, 2010 | value's of the following parameters: Stencil thickness, Stencil apperture, stencil reduction, different PCB manufacturers, P&P pressure and reflowprofile. The only item we have not changed is solderpaste, we now use Almit paste. LT and Almit have also investigated the X-ray pictures in combination
Aug 23, 2010 | Hi, I have never been able to find an acceptable dispense process for dispensing small dots of solder paste. I currently have an auger screw automated dispense system and can not accomplish 0.010" dot sizes. In addition, stencil printing is much more reliable. Your pump or needle is going to plug up often. Maybe you can do it with a jet printing system from Asymtek or MyData. However, I still believe stencil printing is much better than any dispense process. We use electroformed stencils between 0.002" and 0.003" thick with apertures 0.004" to 0.006" square and type 5 paste -500/+635.
Aug 7, 2009 | Hi. We are planning a production run of a board that utilises the SEMTECH SLP2710P8 8-pin device (2.7 x 1.0 x 0.58mm). The part orientation on the board necessitates that the squeegee print direction approaches the stencil apertures on the long side. The apertures are 0.675mm x 0.2mm (0.027”x0 .008”). My concern is paste release, so instead of the usual 0.18mm (0.007”) thick stencil, we have decided to start with a 0.1mm (0.004”) thick stencil. Any thoughts/suggestions you might have to aid me in the right direction so that we can reliably print these critters? We are currently using Indium’s Pb
Feb 4, 2009 | Stencil design (maybe old) question... Hi there, We're developing a DOE where stencil design (aperture design) is going to be evaluated, currently we have regular reduction on sides, home base (triangular and semi-circle), "C" or "U" shape, and an idea for oval shape for pasives also came... Searching on this forum I read that oval shape on the edges for fine pitch is used normally (I have this design for most of my newer stencils), but I want to know if you have experience using oval shape for passive components, mi thinking is that will have better paste release because you does not have square edges, well.. anyways we're going
Mar 12, 2008 | We have a lead free assembly with a 128-Pin PQFP with 20 mil pitch leads. We have tried stencil aperture reductions, step-down stencils, different thickness stencils, various printer setting changes, placement pressure changes, nozzle changes, moved the placement to a different machine, profile
Dec 17, 2007 | printing, as each stencil will be custom to the PCB, eating into the profit. Can anybody suggest an alternative process, make your own stencil and even printer? Whats involved in making my own stencil with a laser cutter. My company wants to sub some work out and I think a Saturday morning in my garage
Oct 10, 2007 | We have done the Green Framed Stencils for an added $50.00 per, then got smart and went to green polyester on RoHS / Lead Free Stencils at no added cost. Dedicated Stencil blades and holders green of course) as well as Green Static mats on dedicated stations with dedicated irons and tips
Sep 18, 2007 | Welcome Jimmy Let's mince words to help focus on the issues. When you say "QFP area solder paste shifted," do you mean: * Paste printed on land pattern perfectly, but moves after printing. * Paste printed off the land pattern, even though the stencil was aligned perfectly with the pattern. * Paste printed off the land pattern, for someother reason, such as poor alignment between the stencil and the pads. Next, what is the occurance of this off pad issue? After that, tell us about the openings on your stencil for the QFP and the pads on the board for the QFP. Finally, we're certain someone
May 24, 2007 | We have a similiar problem with kester em907, a pb free paste. You say that your AOI system picks up blocked apertures, do you mean that the printers own camera looks at the stencil and sees apertures blocked? Or, is it picking up insufficient paste on the pads? When we set up our printer to check the stencil after a print, we seem to always get some blocked apertures, up to 40-50%, but have noticed that the print quality is never really effected by this(assuming we never leave the paste long enough to dry into the apertures). If this is the case you may just want to turn off your stencil
Apr 9, 2007 | Hi, We were running with few defects with lead solder paste. The lead solder paste with stencil 0.010" X 0.020" and 0.004" thick stencil produced near defect free PCB assys. 0.010" X 0.020" (0.004" thick) lead = defect free 0.010" X 0.020" (0.005" thick) lead free = bridges 0.010" X 0.020" (0 will try 0.008" X .012" (0.004" thick)ElectroFormed stencil next. Maybe have to go to type 4 (-400 +500 mesh) paste. Maybe we will switch back to lead solder. Chris
Apr 6, 2007 | .004" stencil. Built the product for 2 years with little trouble. We are now using a 0.010" X 0.015" with a 0.004" stencil with lead free solder and we have 20% failure rate. We are finding a few short at X ray with the lead free. Guess I am going to try 0.010" X 0.010" with a 0.004" thick stencil next. I
Jan 19, 2007 | Pump Stencil Hi I know that pump stencil technology can be used to print adhesive on boards with TH components already placed and clinched, but what about solder paste? The production sequence goes like this: First the jumper wires are placed and clinched with an odd-form assembly cell, then the boards with lots of components really slows the line down. So I was wondering if the pump stencil technology could be applied to solder paste as well, in order to get a large lump of paste on the TH joints but without getting too much of it on the SMD pads. Thanks in advance.
Jan 5, 2007 | we had a lot of problems with bridges, they probably accounted for 60% of our defects. We have replaced our screen printers, our placement machines, our stencil frame system, our solder paste and the way we design stencils. We did these one at a time so we could measure the results of each step . Obviously everyone can not take all these measures but The level of improvement was dramatic. You mentioned upgrading your screen printers, once thats done and you can take them out of the equation, take a good look at stencil design and paste. We use QTS stencils and are pretty happy with them, since you only buy the foil, it makes it a lot more cost effective to experiment with stencil designs. I would not reccomend the brands that only stretch the stencil from two sides as we found those systems to be a part of our problem. I would not get too concerned with your numbers compared with other companies
Dec 16, 2006 | the job on, the results are the same? Are you moving the blades with the job too? Regardless, I'd look at blade and stencil condition and thickness. If your blade is thick (stiff) but worn (no edge), you're at risk of it skidding/skimming and not shearing the paste from the stencil surface. I would think squeegee speed, might also have an effect. If your stencil is worn/striated or dented it may leave room for powder to get under the blade edge.
Dec 6, 2006 | . Problem being short stencil life. Shop around for some other paste that offer long stencil life. Then run a side by side comparison. If this yields no difference then you can rule out paste and try messing around with your humidity. If you DID mean 38 degrees, then your shop floor is just too fricken cold! Spend $30 bucks on a space heater and put it in your screen printer. The penguins may complain but at least your paste will start to roll on your stencil!
Nov 4, 2006 | between paste application and the pc's entrance into reflow. The fresher the paste the better the solder joint. My dilema here is upper management wants the two lines to share one stencil printer thus saving the cost of purchasing a second printer. They propose to paste ahead, allow second runner to change stencils, paste their pc's, and so on. If shifts end approaches, they offer to store the pasted pc boards in a refridgerator overnight until population the next day. Help!! Does anyone out there find this to be a bit odd? Where could I find articles or documentation frowning upon pasting ahead ? If I had something written by an "expert" maybe management would leave me alone and simply purchase a second stencil printer. Thanks for any suggestions you have.
Sep 5, 2006 | Thinking about this auto-mode on Grid-Lok..... Ok, the board is warped, lets say positively, the pins conform to the warped board... what about the effect on top side and squeegee pressure? It will be much higher and could damage stencils, right? Possible, yes? In my view, hard tooling- support pins that hold a fixed distance from the printer center nest to the edge-rail that the board is on is a superior method to deliver uniform print pressure. I want the warped board to be pressed back to as flat as possible when the stencil comes down over it , or board comes up to the stencil. The goal
Mar 23, 2006 | . But you will still see aperture clogging. Stick with the e-formed stencil. For better release, I would go to an 0.004" thick stencil (yours is 0.005"). If solder volume is an issue with the thinner stencil, move your aps back out to the full width of the pad. Type three is always preferred to type four
Feb 22, 2006 | uBGA stencil design We've just set up a couple of products with 0.5mm pitch uBGA devices on them, i went for 5thou thick, laser cut nickel (to aid paste release) square pads same size as the diameter of the uBGA pads. Or you could go to a 4 thou nickel stencil, better paste release on this but you might need to switch to a type 4 paste as you'd get more metal in the apertures to make up for the reduction in paste volume if you've got some larger parts on the board. You could also use a stepped stencil but i'd be carefull with that, not so easy to work with.
Feb 21, 2006 | Stencil past height issue mil or 2 over. Your USL should generally be around 1.5 mils over your foil thickness, so for a 5 mil stencil, 6.5 mils is about right as your target measureent. Then you go about .5 to 1 mil over that. Lower spec limit should be around 1.5 mils less than your target, so a reading of 5 mils for a 5 mil stencil is still within spec.
Dec 12, 2005 | Fine Pitch Stencil Design =roll href="http://www.electronics.ca/standards/general/IPC-7525.html" target="_blank">http://www.electronics.ca/standards/general/IPC-7525.html http://www.alphametals.com/products/stencils
May 3, 2005 | If your image is not defined properly, it will affect positioning and optimization. You can choose center, rear or front image justification. If your values are grossly off, your positioning will be off, and you may not be able to optimize properly, the machine will only optimize Y (stencil ) deviation by up to 50mm. The image positioning is factored in during the calculation to decide where to load the stencil. Positioning and optimization is an effort to bring the image directly above the PCB, minimizing movements and time during production. Since I cannot witness the exact issue, I can only present what the machine can do, and what it likes to do. Anyways, all this will go away as you make the wise transition to 29x29 stencils, the sooner, the better. Happy printing, Mike
Apr 27, 2005 | Hi, There are a number of things you can try. You are already using 1:1 hole to pad ratio, and that's good as you need the size. I would try an electroform stencil as that will have a smooth side of the aperture and help paste release. Don't use chem etched. We had a problem with an old manual stencil printer and went for 4 thou thick stencils, and it helped. So going thinner might help. Use very fine solder paste, and we use Koki fine paste, but there are heaps of brands, and get something for fine pitch parts. You should be able to work with these parts no problems, however it can
Feb 26, 2005 | ], usually 80%. This is because some of these devices operates with high efficiency = temperature. Therefore; the stencil aperture is crucial for this type of package; to much solder in the center and you will have a risk; that one side of the component will be lifted during reflow = no solder joints on that side. There are some cases that the designer has chosen to put via's in the ground pad on the pcb; and that will cause the solder to fill the vias and you will find it hard to fulfil the manufact'rs spec. without to have solder joint issues to the terminals. We use 0.127mm stencil thickness and we have also found out, that the square center aperture in the stencil (ground pad); can be divided into 4 smaller quadrants; the life will then be easier...
Oct 25, 2004 | Stencil Tension Q1: I thought we have a industry standard for this. A1: We're unaware of such a standard. IPC-7525 - Stencil Design Guidelines has a brief section on stencil inspection. We've talked about it previously on SMTnet. If you can't find it in the Archives [seach], say so. Q2: Are you not doing
Sep 15, 2004 | Stencil design for flex-rigid PWB them, so they consume most of that 8 inches in width. This PWB is later folded over a heatsink, sort of like a sandwich. So, to allow the PWB to fold properly, there is a bulge in the flex which won't allow my stencil to rest on the PWB (or even slightly above). It sticks up about 3/8" or so above the surface of the board. Now, the previous engineer had the operators push the center of the flex bulge down as much as possible w/o damaging it, and just let the stencil blade wipe over it. Obviously, this causes problems on those components w/in about 1/2" of either side of where the blade comes off
Aug 19, 2004 | Hi Erhard, Go to http://www.globalstencil.com They are the stencil firm that worked with MPM for developing technology for printing with thick stencils that are milled out on the bottom to account for existing components on the top side of a PC board as well as cut & clinched leads on PCB bottom side. Global Stencil is in Texas and you can speak with Greg Smith. MPM has a machine (UltraPrint 2000) specially configured for this process called UltraDot.
Apr 19, 2004 | The MicroFlex is not really new. Its the UltraPrint 100 re-engineered and improved. UltraPrint 100 / SMTech 100 has been around for many years. I don't believe the DEK 248 offers a Stencil Wiper option. I worked on MicroFlex machines. Vision system is capable of resolving features on a wide range of boards with dark and light solderpmask as well as on ceramic substrates. They are capable of 16mil (0.4mm) fine-pitch and likely below, but I have never tried less than 16mil. Alignment repeatability is +/- 0.005" (0.13mm). Effective fine pitch printing has a lot to do with proper board and stencil design, stencil maintenance, proper solderpaste storage and handling. What else would you like to know?
Apr 9, 2004 | Dish Washer for BGA Cleaning ). Dishwasher �technology� is based on high flow, low pressure. Although flow is one component of thorough cleaning, high-density, low standoff applications such as BGA�s mandate significantly higher pressures than any dishwasher or laboratory cleaner can provide. Anecdotally, my wife reminds me to always rinse off the dishes before loading the dishwasher, otherwise, the dishes may not come clean. The surface of my dishes is free from reflowed components mounted 2 mils off of the surface. The temperature in a reflow oven generally exceeds those of a kitchen oven. Additionally, if using a chemical
Apr 7, 2003 | Russ is correct. A 5 thou thick stencil should give good release. Here's how you run through it: * You want at least 5 solder particles across the smallest aperture. So in your case, 8 thou wide, which equals to 0.20mm gives us 0.20/5=40 microns. That means that you should be fine with a standard Type 3 paste. * You need to consider area and apect ratios on your stencil to get Russ's 5 mil number. [Search the fine SMTnet Archives for background.] So, tell us about your stencil underside wiping approach. As you reduce the width of your apertures, wipe frequency needs to increase
Mar 25, 2003 | features not available on the UP2000, such as an automatic support pin placement system, automatic stencil loading/positioning. The AccuFlex moves the board/ center nest in X-Y-Theta for alignment to the stencil whereas the UP2000 moves the stencil to align with the board, that is fixed in the center nest
Jan 22, 2003 | Stenciling chipbonder..... it without them falling off...... and you've never let me live it down, either. :P "7525, Stencil Design Guidelines is pretty much of a waste." Well, good, because I've lost mine. I don't remember much mention of adhesive stencil design stuff there, as you say. Whatta they stick you for for a 6'er
Dec 20, 2002 | Although everything that has been said earlier is sound advice for achieving good printing results, I strongly believe your problem is your manual printer and its inability to accurately control the speed at which the PCB separates from the stencil after the print stroke. I call this speed the 'snap-off' speed. After the end of the print stroke, a slow snap-off speed (0.5 - 2.00 mm/S) moves the PCB vertically down from the underside of the stencil until completely free of the stencil. This vertical, slow controlled separation I'm sure will overcome your problem. It works for me
Oct 14, 2002 | BGA rework stencils ( down to 0.65mm pitch) Russ, Thanks for the feedback. Yeh, we are placing them in production using a full ball detect Yamaha placement machine, 5 thou square stencil. etc.etc. The only reason I raised this concern was from a rework point of veiw (actually, the board design had the wrong pin out on the board, so we to be sure my placement and ball grain structure is bang on, after rework. Back to mini stencils, can you please provide me more of what you did to get the process working for a design point of veiw. Regards Marc
Sep 24, 2002 | devices will try to tomb-stone. We talked about this before on SMTnet. Search the fine Archives for background. We don't know why you'd want to use a 2 thou stencil. Now if you're talking reducing the amount of solder to reduce variation in the height of components from the board surface that are soldered properly, you are making a BIG mistake. The amount of solder has a large effect on the long-term reliability of solder connections. We don't like to talk about aperture reduction on stencils without knowing: * Pad design * Stencil thickness * Stencil fabrication Closing on stencil fabrication points, consider following the guidelines of IPC-7525 - Stencil Design Guidelines and other references listed in the fine SMTnet Archives. Next, there's no reason why your supplier couldn't print conductive adhesives in a manner identical to the method they used to print solder paste. So, don't buy
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