SMT paste dispenser - Page 1
Forum section: electronics / general

author: elcomtel
author_rank: Regular Contributor
timestamp: October 19, 2013, 03:13:19 am
content: G'Day !I've done a fair fair of SMT rework (except for BGA) professionally and I used to work as a PCB designer where I designed around BGA, QFP, etc, etc. As a PCB designer I used to create solder masks and solder stencil designs.I'm also officially certified to NASA-STD-8739.2 and IPC J-STD-001ES soldering standards. The IPC certification is a joke as there is no practical testing involved. It is all theory and no practicals.Would you believe with such credentials I have never used solder paste in my life, simply because all the SMT work I did could be done with a traditional soldering iron. You would be surprised how much SMT you can do with a standard iron and solder. I can 'drag solder' like a pro, so why the hell would I need solder paste (unless it's a BGA).These days I'm thinking about small scale SMT production and my interest has sparked for obvious reasons. I've sorted out the 'ins and outs' of solder stencils, but the reason for my post is that I want to set up a SMT paste dispenser for development work.Since I have never used solder paste or flux paste I haven't got aPRACTICALclue what I am doing. I have decided to buy a cheap $100 SMT paste dispenser machine from China as illustrated in my attached photo.Due to my total lack of experience with solder paste, flux and the likes I haven't got a clue as to what kind of dispenser needles to buy.I've been able to establish that the following dispenser needles are available.....Needle lengths:6mm, 1/4"12mm, 1/2"24mm, 1"37mm, 1.5"Needle gauges:Spec. Inner Diameter Outer Diameter Colour14gauge 1.55mm 2.10mm Olive15gauge 1.36mm 1.80mm Amber16gauge 1.32mm 1.60mm Clear16gauge --- --- ---18gauge 0.84mm 1.27mm Green19gauge 0.75mm 1.06mm Black20gauge 0.60mm 0.91mm Pink21gauge 0.51mm 0.82mm Dark Purple22gauge 0.41mm 0.72mm Blue23gauge 0.34mm 0.64mm Orange24gauge 0.30mm 0.55mm Purple25gauge 0.26mm 0.51mm Red26gauge 0.23mm 0.45mm Light Brown27gauge 0.21mm 0.41mm ClearNow I haven't got a clue what to buy or what I need.I can imagine that it might be impossible to use a 27 gauge needle with solder flux.I simply don't know.I've never used solder paste in my life.What size dispenser needle gauges and lengths should I consider?Are longer or shorter dispenser needles preferable?I've also seen dispenser needles that are bent. Are they any good?The exercise is to set up a dispenser needle kit as part of my SMT setup.It also occurred to me that the 'dispenser needle' question is relevant regarding my SMT vacuum pick'n'place pen....The cheap $20 kind you buy on eBay. I would imagine that common sense prevails. I would say the largest gauge would be the choice.As for my solder reflow setup my plan is to use a toaster oven and a 10-20mm thick aluminum plate (300mmX300mm) on top of a kitchen type portable electric hotplate. The plan is to use a cheap REX-C100 (see attached PDF) PID temperature controller that you can buy eBay for $10-$20. My toaster oven is a medium sized oven (as opposed to a tiny two sandwich type) so the hope is not to have 'hot spot' problems. The plan is to control the oven and the hotplate with the REX-C100 controller.Please note that I am fully aware of what is expected in the implementation of a 'reflow soldering thermal profile'. The REX-C100 controller is not perfect and the plan is to use it in a semi-automatic approach.ie:- manually set enter the pre-heat temperature on REX-C100 to 150degC.- once 150degC is reached wait for 120 seconds.- manually set enter the temperature on REX-C100 to 250degC.- when oven gets to 250degC wait for 20 seconds.- turn off oven and open front door for cool down.Like I said....semi-automatic SMT reflow oven.I'm mainly interested in feedback about the type of paste dispenser needles I should buy, but feel free to comment about my reflow oven and hotplate ambitions if you wish.Many thanks in advance.

author: sacherjj
author_rank: Frequent Contributor
timestamp: October 19, 2013, 03:36:22 am
content: I just ordered the 982A you have pictured, but haven't received it yet. I've found solder paste to be helpful, even with an iron. Under the microscope, you can use the tip of tweezers to place just a few balls on a very high pitch connector and then iron solder.If you don't have hot air iron, even a cheap one does really well to flow out pasted SMD. I purchased a cheap temperature controlled air pre-heater for $50 that does a good job of reducing the stress during hot air work.I wish I knew how to answer on tips, but I'm looking forward to seeing the responses to help when I get my dispenser.

author: Selectech
author_rank: Regular Contributor
timestamp: October 19, 2013, 04:20:41 am
content: I do a lot of SMT paste work and use a plastic tapered 22 ga { blue } tip with an Ebay shot dispenser I bought a few years ago, similar to the ones pictured.I use Kester R276 dispensable paste for everything.I have a toaster oven with a PID controller. The oven has been modified so the circulation fan stays on all the time and has extra insulation on the top and the door to reduce cold spots. There is a thermocouple that touches the PCB during reflow cyceles. The PID controller has profiles that can be set and I periodically check the profile with a logging program. I do many hundreds of boards a year in this thing and it's been doing well for 5 years now.I tried the hot plates & skillets but the toaster oven wins. I never leave the oven un-attended when running cycles but I can do other stuff when a cycle is running - although it only takes about 3 minutes for a cycle. No real need to watch it - it just does it's thing every time and beeps when it's cycle is done. Open the door to cool down, then an oven mitt to pull things out. I have small wire mesh trays for some of the smaller things I do, 10 to 20 pieces at a time. Larger parts are only 1 or 2 at a time on the oven rack.I also have a 2nd dispenser setup mounted on a small cnc machine for pasting up my production cards. That has also been going for 5 years. Yes, it is slower than a paste mask, but there are no masks to make or clean and solder paste waste in practically 0. Also, I can do other stuff while a board is being pasted. Changeover from one board type to another is a few seconds.To keep compressor noise down I use a small tank compressor for airbrush work. Reasonably quiet compared to the nail gun compressors at the DIY shops, it has lots of capacity for the shot dispenser.For the vacuum pen, I use a small 24V DC vacuum pump { small & fairly quiet } and various needle tips that fit / hold the parts I"m placing. I just use straight tips as they work well for me. I tried the aquarium pumps but found them marginal and finicky. A decent pump reduces the number of tip sizes changes that are needed. I also have a foot switch to run the pump.As mentioned by others, I also use paste with an iron for some kinds of assembly. I do have a hot air tool and use that as well, but try to do most everything with the toaster oven. I do have some small double sided assemblies that use the oven for 1 side and teh hot air tool for the other.

author: george graves
author_rank: Super Contributor
timestamp: October 19, 2013, 06:32:48 am
content: Quote from: sacherjj on October 19, 2013, 03:36:22 amCan you explain a bit more about what a pre-heater does for you? How does it help?

author: Kjelt
author_rank: Super Contributor
timestamp: October 19, 2013, 09:55:17 am
content: QuoteI had the same problem 2 yrs ago when I started, let me share my personal experiences concerning the needles:The needles are one time use only. You can go and clean the metal ones if you want to but that is messy and lots of work, tried it two times then stopped, not worth the hassle.The inner diameter is the size of the paste coming out and ideally should match the trace width of the PCB isle which depends on the SMD package.If you follow that then you should have a lot of needles in stockwhich is not very handy and affordable for a small production/hobbyist way of working and discard them all.So what I have finally came up with for myself is not buy the metal needles but the plastick ones and almost the smallest size (believe 26 i have).Use that for the smallest arreas then use a Stanley knife or better surgeon knife and cut off a small portion of the tip, the tipsize will be somewhat bigger and continue with the bigger arreas and so on till the final ones. This works pretty neat for a few pcb's and you need to finish it within 2 hours or the paste dries out.If your serious and working a few days in a row it might be better to buy three different sizes of metal needles but not too close too eachother in gauge, difficult to advise since it all depends on which parts you're using.My personal experience with the dispenser is not very very good, it works but there are a lot of variables involved: temperature and thus the liquidity of the paste, the pressure, the vaccuum backdraw. So often with my dispenser experience (old multicore) it takes long time before paste comes out and the amount is correct and even then it sometimes keeps on oozing slowly out which I find very annoying. It's lead based you don't want to get it on your hands or equipment and I am a bit of a neat freak in that area.So when I have to do a lot of identical pcb's with more then 20 SMD's on it I order and use a stencil and use the different paste (bigger lead balls) that is cheaper and comes in a jar. That works great for me, just smear it over and place the components.Then when finished I clean the stencil first with fluxremover then with IPA.just some last tips: Use gloves when possible, and a have roll of kitchen paper in the vicinity and an empty trashcan with bag for leadbased garbage disposal, when reflowing ventilate well cause it smells and is unhealthy.Other subject you mentioned is the vacuum pickup. My personal experience the pasteneedles are not very usefull for that purpose.I bought the needles with suction cap that can be bought seperately for instance Farnell: EDSYN Ordercode: 844494That is 3,0 mm I am myself still looking for even smaller ones (1,0 mm) so if somebody reading this has a tip for that I would appreciate itGood luck and enjoy.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 19, 2013, 11:27:15 am
content: Quote from: Kjelt on October 19, 2013, 09:55:17 amBut they are dirt cheap these days. Example 100 pcs for $4.75http://www.ebay.com/itm/100-x-Dispenser-0-6-Gage-0-6mm-OD-Glue-Liquid-Dispensing-Needles-Tips-/321142551120That is less than five US-cent / needle.

author: Kjelt
author_rank: Super Contributor
timestamp: October 19, 2013, 11:31:43 am
content: Quote from: Bored@Work on October 19, 2013, 11:27:15 amIndeed I have only been looking at OKI/Weller needles at Farnell. So then this might be a good nd cheap alternative.For TS: Most important to watch for is that the needles do have luer lock otherwise the pressure will blow the needle off.

author: Alphatronique
author_rank: Regular Contributor
timestamp: October 19, 2013, 02:13:14 pm
content: Himy opinion ,forgot solder paste dispensing ,past dispenser was good for flux dispensingif need to solder BGA just put Tacky Flux put BGA on it center , and reflow it ..and if you what to build more that a board take very thin aluminium sheet (bit thicker that coke can) ,print solder past on paper then mark pad center with needle then drill with 1mm drill bitsand and you got nice solder paste stencil , work good but still need to solder 0.5mm pitch IC by hand ,but all passite will work great and whit consistency ,and far better that whit hand dispenser or even a past dispenser robot ..p.s. only way to have good consistency was use a auger valve dispenser head but it cost 5K$that because solder paste was made for be "thixotropic" ,so it viscosity change over pressurethat desired effect for stencil printing but really bad on air driven dispenserBest regard

author: tsmith35
author_rank: Frequent Contributor
timestamp: October 19, 2013, 02:27:31 pm
content: Quote from: sacherjj on October 19, 2013, 03:36:22 amWhich pre-heater? I have a couple of larger IR heaters, but it would be nice to have something smaller (closer to a Zephyrtronics Airbath) for smaller areas.

author: sacherjj
author_rank: Frequent Contributor
timestamp: October 19, 2013, 04:02:38 pm
content: Quote from: george graves on October 19, 2013, 06:32:48 amI'm using this one:http://www.mcmelectronics.com/product/21-10135I've found that without it, I have to hit a part pretty hard with the hot air iron when soldering or reworking. With a preheater, I can slowly bring the board up to maybe 100 degrees under reflow temp, so it doesn't take as much hot air to melt the solder for reflow or part removal. I'm much less likely to damage a sensitive part that is near by. I've seen hot tolerance parts go out of tolerance when having to replace something nearby and cooking too much with hot air.

author: tsmith35
author_rank: Frequent Contributor
timestamp: October 19, 2013, 04:08:02 pm
content: Cool... thanks!Got one ordered... used their 15% off coupon (AFC909). Should be a pretty nice addition for the many small boards I end up working on.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 19, 2013, 04:28:39 pm
content: I prefer the stainless needles to the tapered plastic ones - I find the tapered ones clog easily.You also waste less paste when you do throw away a blocked one.And foot-pedal operation for a dispenser is essential. Ditto vacuum pen.

author: elcomtel
author_rank: Regular Contributor
timestamp: October 22, 2013, 11:43:28 am
content: Thanks everyone for your feedback. You input has truly been invaluable.Re. my toaster oven as SMT reflow oven.I just ordered a SPI (MAX6675 device) thermocouple module with K-type termocouple on Aliexpress.http://www.aliexpress.com/item/Free-delivery-MAX6675-thermocouple-sensor-type-K-thermocouple-module-thermoelectric-coupling-electrode/1118737884.htmlI'll use it as the basis of the oven temperature control.It might also be the way to go for a SMT hot plate.

author: Psi
author_rank: Super Contributor
timestamp: October 22, 2013, 12:04:27 pm
content: make sure you keep your solder paste in the fridge when not using it.