Reflow PBGA

Steve,

I'd second Daan's opinion.

BGA profile we use gets a peak of 210deg-C to 223deg-C (but that's using our WS paste unique characteristics) with reflow zone holding time of 45-60sec. We had 6 PBGA and 2 ceramic BGA on a 6 layer PCB.

typical profile we see gets a 230deg-C peak reflow temperature. Check with your paste supplier, for their lab qualification settings during the conceive period of your paste type's reflow profile.

Check whether your paste reflow can go to 230deg-C? that shd give your PBGA around an ideal 218+/-5 deg-C beneath it.(from our experience, go do your own tests)

your oven delta-T capability will also influence this reading, just as the connection of your (K-type?) thermocouple linked to the BGA balls you are profiling (you are profiling from the BGA central ball ain't you?).

Oh! Oh! and to sum it all up, go check the fine SMTnet archives.

reply »

Steve,

Dason has valid points here.

dun listen to what supplier's say about paste lying on the PCB pads able to be exposed at ambient temperatures for 8-24 hrs? that will never get approval for Class-3 type of customer auditors. (Would any serious process owner leave printed boards lying around in the shop-floor for that amount of time, and not process the boards thru the oven?)

Know your machines and know your materials, and all the poor soldering joints can be solved.

We control our WS paste no more than 6hrs exposure time in the stencil. Labels on the paste-Can, assist in the FIFO control and traceability if need be on the Can-opening time.

check your supplier for B&W instructional specs, not some verbal promise in performance.

Good Luck!

reply »

Go to the top of the page and enter your topic in the "Search SMTnet" window. It can take some tweaking to get it dialed in to the exact topic you want.

Do you mean the paste was on site for 3 weeks, or was it actually out of the fridge for 3 weeks? We try to keep our "out of fridge" paste quantities at about 2 days worth because the room temp shelf life is about 1/4 the refrigerated life.

I couldn't find anything on the Alphametals site on your paste, but if you leave containers out of the fridge for three weeks, or leave your containers open all day, or leave it on the stencil all day (or on boards without reflowing for that matter) I think you're asking for trouble.

reply »

Steve, I suggest to review some of the paste handlering procedure from some of the supplier. Aim look have a better procedure for our industrial but you need to check with your paste requriement. ie. Indium can store the paste @25C for 3 mths???

http://www.aimsolder.com/techarticles/Handling Solder Paste Article- manuscript.pdf

reply »

Hi mate,

suggestion: consider "re-fridge" the paste after each Lot (small volume) batch run, instead of leaving it at ambient temperature for 3mths. follow FIFO control of such re-fridged paste. check with your supplier (in documented format reply) what is the procedure control for repeated use of the "out of fridge" paste?

Note: correct us if we have got your points wrong, thanx.

reply »

Hi mate,

"no more than 6hrs in the stencil" for us means:

1) we finish setup of reflow oven, P&P m/c, and lastly the printing machine(includes loading of stencil into printer machine).

2) once printer machine is setup, we rip-open the paste Can protective seal, and pour the paste onto the stencil. we record the "use time" onto the FIFO label (label attached to the Can).

3) For the WS paste we use, its a special formulae we commissioned for our own use, and supposedly has a 8hrs exposure(usage time) to ambient tempeatures. we set 6hrs to give buffer for machine downtime arising from dilly-dally and some setup debug timing for the Technicians. Your supplier will have their own set of "usage time" specs.

Heyz...no need to for the mush. all of us previously started somewhere at the bottom, and then worked our way up. life is not only how hard you work, its also about all the opportunities that other people shared with us. remember those people. Cheers!

reply »

Hi mate,

there is another thread ongoing about such an BGA vs oven length issue, suggest posting your question there.

As for that someone's opinion, he/she is entitled to it. Then again how did that someone determine this level of "insufficient"?

It could be my stubborn streak ingrained into my genetic makeup, I believe its gonna be "harder" to get the same profile on a 5zone compared to a 12 zone Oven, then again I'd gain great professional satisfaction in making possible what was "insufficient" and difficult for that diapproving other person.

reply »

Forgot to include the following:

Dwell time is from 55 secs to 68 secs. Indium specs for the paste is maximum peak @ 228'C and 30 to 90 secs dwell time above 183'C. PCB is a 6 layer board with Dimension of 205 x 166 mm but is slightly dense with 11 SMT Relays, 1 PLCC44, SMB's,0603's, 0805's, Tant Caps, 4 Dpaks, SMT Bridge Diodes, SOIC's etc. PCB design is quite good as the PBGA is place at the center of the PCB. It is also a double sided PCB using Glue @ the bottomside and passes the Wave Soldering Process after manual insertion of PTH Components.

regards,

reply »

Is that 5 top and 5 bottom zones? We use a 4 zone and a 3/4 zone oven for BGAs and have success. I don't believe that the amount of zones is the issue but what type of profile you can get out of them. I will admit that the large ovens are much easier to profile than our little "tabletoppers" but if the oven has good convection it should work. When you profile a board do you see a lot of temperature difference across the board at different locations? If not you will probably be fine. I also work at a C.M. and I should be telling you to send your BGA work to us since "you aren't capable with your oven" but I won't

Russ

reply »

You guys are really helpful. Thanks again for all your suggestions.

This message was posted the Electronics Forum @

reply »

WE USE A HELLER 1500 EXL OVEN (5 ZONE OVEN) AND HAVE BEEN DOING PBGAs FROM 292 TO 780 BALLS WITH .O32" PITCH (.8 mm) AND METAL STIFFENERS ON TOP WITH NO PROBLEMS. I AM GETTING 210 - 215 DEGREES C AT THE BGA BALLS WITH 50 - 65 SECONDS ABOVE LIQUIDUS DEPENDING ON BOARD AND BGA SIZE. OVEN SETTINGS ARE IN C: 150,170,180,190 AND 250 AT 54 CM/MIN. WE HAVE FOUND OUT THAT BGAs ARE EASIER THAN .015" PITCH FINE PITCH PARTS. HOPE THIS HELPS.

reply »