Soldering 0.4mm bump packages - Page 1
Forum section: electronics / projects

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 01:47:36 am
content: Has anyone here successfully soldered 0.4mm pitch bump packages?I have a 4x5 that I am hoping to do. I will order a stencil from JLCpcb. Will this be thin enough? They don't state their stencil thickness. just remembered I have bought stencils from them before. The last one I got was 0.1mm and I ordered it electropolished. I worked Ok I guess, but I wasn't doing extremly fine pitch with that one.I have a reflow oven and am planning to use leaded T4 paste (183°C)The smallest I have done up till now is 0.5mm DFNAny hints or tips gratefully received.Thanks,R

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: July 05, 2018, 03:43:05 am
content: I recently did a handful on myfrequency counter. The PLD's are 0.4 36-WLCSP packages (MachXO3). I'm no expert so will just offer what worked for me.First gather as much data about your part as you can. Lattice have lots of information on package dimensions, layouts and soldering temperatures and so on.The main considerations for the PCB layer (aside from breakout) is the finish pad size and if the pad is going to be solder mask defined (SMD) or non-solder mask defined (NSMD). Ultimately I went with NSMD 0.25mm pads really just because that's the size given in my datasheets.The BGA balls are themselves solder the datasheet again will tell you what the peek temperature you need to get to, this is not just determined by what paste you are using. For me that was 250°CI had previously tested my oven could manage that by unintentionally setting fire to a scrap FR4 and completely stinking out my houseNext while reading how to make these things stick online all the advice was that despite the balls being solder you need at little flux to remove oxides and get things started. So if I did not read that I was going to not allow for the BGA in the stencil at all.Having said that I did not want to a separate paste / flux pass on my board so I decided to use solder paste for everything given it's mostly flux anyway I figured it would be fine. I used an unleaded paste with the smallest ball diameters I could find so that enough of them would get squished through the tiny holes I was going to have in the stencil. [will link in if I remember later]Once that was decided I made the stencil such that the BGA holes were 0.2mm or at least something smaller than the landing pads on the PCB, this was my method of controlling the amount of paste/flux that gets applied.I ordered the stencil with metal frame 0.12 mm thick (their default for PCBWay).Once that all arrived the hardest thing was lining up the stencil - this I normally do by hand with a bright halogen lamp directly above my head until I see the flashes of gold in every hole.Also a challenge was that the silk screen, that I was going to rely on to place the BGA, was registered badly so I had to manually compensate for that.Deciding not to freak out on my first attempt I just resigned myself to a fail got the part as close as I thought to the pads. I figured this would be no different to any other SMD part and surface tension would fix everything.Cooked in the oven and everything seems to work out fine.

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 04:29:33 am
content: Thanks David, That's all great information to think about.I didn't think about having to use an unleaded profile to melt the balls. So you saved me some parts there

author: mark03
author_rank: Frequent Contributor
timestamp: July 05, 2018, 06:08:16 am
content: Following this with interest as I am about to try the same thing. In my case, some 2x2-ball bare-die MOSFETs (EPC GaN parts). I am planning to use flux only, no stencil or paste. Electric hot plate for pre-heat to ~150C, then hot air to reflow.I am a bit worried about part alignment as +/- 0.2mm doesn't seem like a lot. I am also unsure of the optimal distance for the hot air nozzle... super close and aim for the part only, or a bit further away with a larger nozzle to heat up the whole area?

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 06:15:09 am
content: I tried to do DFNs with hot air once. Was a disaster. No matter how soft I had the air on, they would blow away once the solder melted. I think it might have been because it was quite a tall device compared to the width.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: July 05, 2018, 06:53:46 am
content: The solder paste I used was Chipquik SMD291SNL50T3 - SnAgCu balls <45um melts@220°C re-flow temp 249°C. I'm not saying it's the best for the job, just the one I used and had decent results with.If you've done the PCB already I'm sure you have battled with the pcb-fab capabilities, I had a lot of back and forth emails with pcbway and in the end I think they contracted it out to some one else. But 'dog-bone' fan out was, well, out of the question. So I did via in pad, they filled them with a conductive resin and capped them. The capping is nice because you end up with a perfectly (as far as I could tell with my microscope) flat and hopefully level pads.If you do via in hole and do not fill or cap then expect problems.. or do it anyway and get luckyI was listening to theLuke Valenty interview(of TinyFPGA fame) who surprised me when he said he just ran traces under unused balls and all sorts of things that would be considered hacks by anyone who has done 'proper' fan out but he was just working within the limitations of the PCB fab, and doing so keeps the cost way down.As soon as you go a smidgen over the design limitations no one ever says no they just charge you an arm and a leg (well relative to the prices we've come to expect from cheap prototype houses)Anyway... My eyes are in no way up to the task so use a camera scopelike this onenot exact model so can not recommend. I did most recently purchasethis onefor my works service department. They plug in to a standard VGA or HDMI monitor. I must prefer these to squinting in to eye pieces, and can not afford a Mantis or equivalent.Quote from: mark03 on July 05, 2018, 06:08:16 amMark, I've only ever had the exact same experience with hot air, as soon as the flux heats up it's viscosity drops creating 'ice rink' conditions on the pcb. I've been using a very cheap toaster oven with all manual controls for years now and everything always comes out perfect..disclaimer 'perfect' comes from trial and error first boards I did had no thermal relief on some pads and those parts tombstoned in reflow. Other issues around having too much or too little solder relate to pad sizes, solder mask expansion and stencil hole sizes and placement. But I've never had anything go seriously wrong.If the 2x2 ball MOSFET is the only part on the PCB then hot air might be the way to go but I've found it much simpler to stencil the design, wipe solder paste on every pad, casualty place all the component while sipping an ice tea and baking in the oven for 4 minutes or so.

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 08:34:33 am
content: I haven’t made the board yet. I was planning on using pcbway. They claim they can do filled and plated vias at 150 micron.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: July 05, 2018, 08:51:25 am
content: Mine ended up as 0.15mm traces, 0.15mm via and 0.25mm pad size as mentioned previously and 0.14mm clearance. This still exceeded PCBWAY capabilities but they spun it for me all the same and as far as I can tell (without dissecting one) it all checks out.Here is my fan out, note I also got away with the fat spacings because I did not need to bring out all pads. None of the Vias are blind or buried that's a whole new brave world for another time I think.

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: July 05, 2018, 09:03:38 am
content: Yes thats why i filled and capped mine. I mentioned that if you ignore that advice you might get lucky for a few home made ones but expect your production yeilds to be low in higher volumes.

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 11:06:21 am
content: Pcbway told me that they can fill and plate the pads.

author: bson
author_rank: Unknown
timestamp: July 05, 2018, 04:40:43 pm
content: Quote from: David Chamberlain on July 05, 2018, 06:53:46 amNice. I could use this - any thoughts on what to ask for and how to mark vias that should be filled and capped?

author: David Chamberlain
author_rank: Frequent Contributor
timestamp: July 05, 2018, 08:51:53 pm
content: Quote from: bson on July 05, 2018, 04:40:43 pmA lot of this was organised via email after I posted the order. They do have a "Additional Options" section on the quotation/order page and the relevant options such as "Via in pad" and "Via filled with resin", but they don't have a box for capped vias on that page.Now that I read back at the emails I think the two things are mutually exclusive and you can have either resin filled or electroplated copper but not both. So I guess what I really asked them to do in the end was electroplated copper only.I did not specify on the Gerbers anything special about the vias nor did we discuss that via email, they just capped them all. I don't know if it's cheaper or more expensive to selectively cap (plate?) some and not others but mine were all the same size on the board anyway.Getting to the limit of my knowledge here, and not wanting to butcher pcbways reputation with my ignorance, I would suggest just place the order and then email them any additional questions. You are not obligated to proceed till you fork over the cash at the end of the design review.I needs to be said of course that this applies to any pcb-fab and I'm not personally endorsing pcbway over any other. I've also heard good things about jlbpcb as well.

author: Teledog
author_rank: Regular Contributor
timestamp: July 05, 2018, 09:52:24 pm
content: Do you mean BGA?Never heard of "bump" packages.Installed/replaced countless NAND & CPU BGA chips in the past.If you're ordering a board(s), you might want the vias "tented", usually at no extra cost.I've never used stenciled paste/solderball-type flux when installing BGAsAlways make sure the pads are microscopically clean, wipe rosin flux (pen) on the padsFlux the "pre-balled" BGA device with the rosin pen also.Place the BGA on the pads, the chip should essentially stick to the rosin.Pre-heat from underneath & heat the top with a very hot,low flowheat gun (not a rework hot air unit)We used a hardware store heat gun with a fan dropping resistorShould be ~250-260C with an IR themometer when things start to happen (and very quickly)The chip will slide (sub-millimeter) into place when the balls melt.. & keep the heat on for another few secondsG'luck!

author: Geoff_S
author_rank: Regular Contributor
timestamp: July 05, 2018, 10:10:51 pm
content: I know PCBWay offer via tenting, but what would they tent with ? For some reason I thought they plugged the vias and covered the top with soldermask...

author: Dubbie
author_rank: Unknown
timestamp: July 05, 2018, 10:22:34 pm
content: If you click on the "via in pad" (?) icon, it tells you that they are epoxy filled then plated overtop.Regarding "bump" vs BGA nomenclature,Bump seems to be used when talking about Wafer Level Packaging (WLP)The solder bumps are directly fixed to the silicon.More information here:https://www.maximintegrated.com/en/app-notes/index.mvp/id/4002