Leadless package placement assistance - Page 1
Forum section: electronics / general

author: jeremy
author_rank: Super Contributor
timestamp: October 30, 2017, 12:50:30 pm
content: Hi,I'm looking for something to help with leadless package placement (as in packages with no leads or legs, not leadless a la RoHS). I'm interested in everything from BGA/QFP/DFN/LGA/WSON/etc or even as small as WLCSP if I can get away with it. Ideally 20-25mm square BGA as the maximum size (but I won't complain if it is larger). Essentially I'm trying to minimise the risk as much as possible without getting an xray.I am perhaps thinking of a pick-and-place, but I don't really need the feeders and what not. Just placing valuable ICs accurately. I realise that pick-and-place machines are very cool, but I'm not sure I have the space for one.Does anyone have experience with this? Any ideas?

author: ovnr
author_rank: Frequent Contributor
timestamp: October 30, 2017, 12:54:55 pm
content: Smaller stuff: Just do it by hand.Bigger BGAs: There are BGA rework stations that will do the whole job for you. They're stupidly expensive.

author: jeremy
author_rank: Super Contributor
timestamp: October 30, 2017, 12:56:03 pm
content: Thanks, but do it by hand is my current approachI'm looking to make it a bit easier and more reliable.

author: Kean
author_rank: Unknown
timestamp: October 30, 2017, 01:02:42 pm
content: I presume you're thinking in terms of prototypes, so just small quantities that you can't justify sending out to an assemblerIf so there are BGA inspection camera systems available, but you can possibly also just use a small mirror with a microscopeBut they quickly get very expensive!From a quick Google...http://www.optiliaindustrial.eu/products/product/30/30http://caltexsystems.com/products/bga-inspection-system/bga-inspection-mirror/

author: elecman14
author_rank: Unknown
timestamp: October 30, 2017, 07:48:00 pm
content: I would also recomend BGA inspection mirrors. Something like this helps show if the BGA is lined up with the pads.http://www.techni-tool.com/550SO840A goose neck microscope light and flashlight are also quite handy to light the bga when using the mirror.

author: asmi
author_rank: Super Contributor
timestamp: October 30, 2017, 08:16:55 pm
content: Make sure that your silkscreen outline is just a bitoutsideof package's bounds, so that you can see the line with package installed - at least in the corners. Then use it during placement as a guide. This is especially helpful for big BGAs which don't fit within microscope's field of view. Also please note that the placement doesn't have to be perfect as package will realign itself during reflow if placement error isn't very large - most packages will tolerate errors up to 0.2 mm or so. I assemble my boards myself with a pickup tool powered by vacuum pump under cheap stereo microscope, and I can easily place components down to 0402, and currently I'm about to try using 0201 on a first "real" design (tried that on a small test board before and it was OK). My boards contained BGA, QFN, CSP, LGA, QFP+tab and some other tricky packages, never had a failure yet, but did have few close calls where shorts were found during post-reflow inspection (it was caused by too much paste dispensed). Also - unless you absolutely can't - I recommend using leaded solder paste as it's much easier to work with, and it's surface tension force is higher than that of LF paste, which aids self-aligning of components during reflow. And - finally - NEVER skip or cheap out on post-reflow inspection! It saved my bacon almost more times that I'm willing to admit!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 30, 2017, 09:40:41 pm
content: Quote from: asmi on October 30, 2017, 08:16:55 pmSilkscreens aren't always aligned as well as you'd like - marks on the top resist may be more reliable

author: asmi
author_rank: Super Contributor
timestamp: October 30, 2017, 10:02:13 pm
content: Quote from: mikeselectricstuff on October 30, 2017, 09:40:41 pmLike I said, it doesn't matter all that much because slight misalignment is acceptable. I'm yet to encounter boards with such big offset (bigger than 0.2 mm) so that it will be an issue. But if electrically boards are OK (so only slikscreen is offset) and I only intend to build one or two prototypes, I'd add alignment marks manually.

author: jeremy
author_rank: Super Contributor
timestamp: October 31, 2017, 04:04:28 am
content: Hi guys,Thanks for the suggestions. I do indeed add alignment marks to the silk, and I normally do all of this by hand. I'm only concerned because I'm starting to do designs where both the prototype boards (many layers) and ICs (SoCs and FPGAs) are quite expensive.But if nothing exists, I guess I'll need to keep doing it this way, or make something myself.Thanks,Jeremy

author: D3f1ant
author_rank: Frequent Contributor
timestamp: October 31, 2017, 07:18:46 am
content: Most parts are designed to float into position, even if they are quite a way off (ie a few 0.1mm's)Follow the datasheet recommended footprint and stencil design.

author: asmi
author_rank: Super Contributor
timestamp: October 31, 2017, 02:15:22 pm
content: Quote from: jeremy on October 31, 2017, 04:04:28 amI'm in the same boat as you, with my first 6-layer board is being manufactured right now, and BOM cost for a single board closing in on $200. I would advise you to try it out first on cheaper components if possible - for example buy the cheapest FPGA that is pin-compatible with the one you actually want to place, and try soldering it. Since you probably receive several PCBs for whatever project you have in mind, sacrifice one board for experiment by only soldering a bare minimum of components to see that you didn't screw up layout (yea, been there - done that). Basically you need to build confidence that you can do that. I did this myself with (relatively) cheap XC7A15Ts, as well as some SPI Flash and HyperRAM chips (all in BGA packages) to just get used working with them, so that I will have more confidence in positive outcome when I place in $120 FPGA chip.

author: elecman14
author_rank: Unknown
timestamp: October 31, 2017, 03:11:32 pm
content: Quote from: asmi on October 31, 2017, 02:15:22 pmIf you want to do verification Topline has a large number of dummy BGA's that have the pins tied together internally. With the correct PCB these can be used to verify your BGA process. Here is a linkhttp://www.topline.tv/bga.html

author: asmi
author_rank: Super Contributor
timestamp: October 31, 2017, 03:35:05 pm
content: Quote from: elecman14 on October 31, 2017, 03:11:32 pmIf all balls are tied internally, how can I verify that there is no shorts if whole chip will be shorted out? At least in case of FPGA I can use JTAG boundary scan (or just create a dummy bitstream that toggles all pins) to verify that soldering was OK...

author: ovnr
author_rank: Frequent Contributor
timestamp: October 31, 2017, 04:58:58 pm
content: Quote from: asmi on October 31, 2017, 03:35:05 pmThey're not all shorted together. See theTopLine catalog- in short, the pins are daisy-chained together. If your PCB also daisy-chains the pins, but off by 1, you end up with a single long string of junctions. If you do a continuity test on it and it passes, it means all the solder joints are successful.

author: asmi
author_rank: Super Contributor
timestamp: October 31, 2017, 06:26:47 pm
content: Quote from: ovnr on October 31, 2017, 04:58:58 pmI see - so it requires specifically-designed PCB. It still won't help to detect shorts, but it will allow to detect solder failures (as in not-soldered balls).Still it's interesting idea. The only thing - I couldn't find any pricing information on the website

author: elecman14
author_rank: Unknown
timestamp: October 31, 2017, 07:39:47 pm
content: Quote from: asmi on October 31, 2017, 06:26:47 pmIf you did a fan out you could detect shorts between the pads. Probably not worth doing but possible.Last time I ordered you just emailed the sales contact (sales@TopLine.tv) what you wanted and they got you an invoice. Not sure on what the price was since my employer was paying for it.

author: asmi
author_rank: Super Contributor
timestamp: October 31, 2017, 08:13:40 pm
content: Quote from: elecman14 on October 31, 2017, 07:39:47 pmWell for me the price is everything since I will paying for that out of my own pocket. Unless I know the prices (at least approximate) I won't bother talking to sales.

author: ovnr
author_rank: Frequent Contributor
timestamp: October 31, 2017, 10:21:41 pm
content: Quote from: asmi on October 31, 2017, 08:13:40 pmI don't know the exact prices, but for simpler packages (SO-16 and the like), I'd expect them to be more expensive than jelly-bean parts. For larger BGAs and the like, I'd expect lower prices than what you'd usually find in that package.These are for characterizing and testing soldering lines in a repeatable way. Since you'd need a dedicated board for them, I doubt it's worth the extra headache.All in all, I'd expect you will have bigger issues with the circuit/board layout than you will have with soldering, at least if you look at it from a cost perspective - reworking the odd part versus re-spinning a whole board that's unsalvageable.

author: KL27x
author_rank: Super Contributor
timestamp: November 01, 2017, 08:27:45 pm
content: I made a simple tool for placing parts like this, back when I was still trying to use solder paste.It's about a 2 foot long piece of dowel with some handles placed on either end. A hole is drilled right at the middle of the stick to place part of a 3mm syringe. A long syringe needle with the rubber IC pickup attachement is put on the syringe. And the vacuum line is plugged in the other end with some creativity. Another hole is drilled just under the pickup needle to hold a "foot," which is just a piece of thick aluminum wire, which is sturdy but malleable with needlenose pliers. A bit of rubber tubing is slipped over the wire for traction.So the idea is you set down the foot next to the footprint and then lower the chip onto the pads by rotating the stick forwards. You have to tweak with the angles and the foot to get it just so, to where with that thickness of IC the chip ends up level with the pcb just when it grazes the top of the pasted pads. So once you get the foot set in the right spot, you can place and drop the part (with foot pedal) without any shaking.It is a bit of a hassle to use, but I consider it a success. The stability is very good. But I gave up using solder paste for my leadless IC.* I don't do BGA or multilayer boards, yet, so I don't know what that takes. But for QFN I prefer to just put solid solder onto the pads, add some more flux, and reflow the chip on with hot air, pinning it down with tweezers until the solder flows. As long as the pool of flux is sufficient, it's not particularly fiddly. After a year of doing a modest quantity regularly, I tend to put a little extra solder on the center pad and just squish it firmly to the board when it reflows. The excess solder ends up just jumping to one or two of the outer pads; I clean that up, after. I wonder what happens to a BGA if you tried to do it this way. They don't have a big center pad, but I wonder if you tinned the pcb pads and also tinned the BGA you would get some excess solder to squish around. If you did that and added some escape pads around the footprint, I wonder if that could help. I have inkling that the major problem with BGA is the multilayer board makes hot air wand inadequate.*Actually, all IC. I have so far failed to learn how to paste accurately enough to bother with any IC. I can do paste stencil good enough to get 99% of the passives on correctly, 99% of the time. When I try to up my game for IC, I can not keep the quality high enough without adding more effort than it's worth. I think I gave up before finding a good paste. I tried a couple name brands, only. And a couple of the cheap Chinese kinds. Then I just started removing IC from my stencil layer.

author: jmelson
author_rank: Super Contributor
timestamp: November 01, 2017, 09:32:54 pm
content: Quote from: ovnr on October 31, 2017, 04:58:58 pmBut, that DOESN'T mean there are no shorts between balls. It only detects no OPENS.Jon

author: jmelson
author_rank: Super Contributor
timestamp: November 01, 2017, 09:39:09 pm
content: Quote from: KL27x on November 01, 2017, 08:27:45 pmI do lots of SOIC-type chips with excellent results. I did learn you have to reduce the aperture size to smaller than the pad size, and use .003" thick stencils. I do chips down to .5mm lead pitch, but do have occasional bridges between the pins on those chips. I never have bridges on the SOIC parts. I make my own stencils from .003" brass shim stock, just like etching a double-sided PC board. I did make a laser photoplotter with 1000x1000 DPI resolution, to make the master artwork.I have made over 1000 boards with this system in the last 10 years. The very first, before I had figured out the aperture reduction was a little rough. I do have a high-end P&P machine that handles the ICs quite well.Jon

author: jeremy
author_rank: Super Contributor
timestamp: November 02, 2017, 02:41:38 am
content: Quote from: jmelson on November 01, 2017, 09:39:09 pmI'm very interested in your stencil system! Do you have it documented somewhere? if not, could you share it in a thread on this forum ?