Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


solder balls

Antonio

#5171

solder balls | 7 February, 2001

I've recently read a posting here which said that the person was trying to reduce solder balls. One of the things the person had done was to adjust the reflow profile so as to be hotter and longer in the reflow state. Am I wrong here? I thought that would only INCREASE solder balling. I am under the assumption that REDUCING the temp and liquidous time in reflow would help reduce solder balling, not increasing. Who's right?

Antonio

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#5179

solder balls | 7 February, 2001

Every critter out there with large incisors adapted for gnawing and nibbling has a different theory of solder ball formation. [My theory: It�s punishment for using NC fluxes. Stand and deliver. My solder balls end-up in the gross filter connected to the out-bound pipe of my in-line cleaner.] Personally, I try to stay out of these solder ball [orzit bull] sessions, but can�t resist this one.

Antonio, why does it even matter what the liquidous temperature is or how long it stays at liquidous, if flux starts to volatize at 150�C?

"Hotter And Longer In The Reflow State Theory" is attractive because it provides the time and temperature necessary to evaporate all solvents and increase wetting. Er is it that it�s unattractive because fast coalescence will trap the boiling flux allowing it to explode and spread the solder everywhere?

"Antonio�s Reduced Temp And Liquidous Time In Reflow Theory" is attractive because the lower temperature does not get things too hot. Er is it that it�s unattractive because slow wetting and reduced drying time will trap the boiling flux allowing it to explode and spread the solder everywhere?

For a fairly reasonable look at the issues, check SMT Magazine, April 2000, V14, #4, p51-58 "Minimizing Solder Spatter Impact" [http://smt.pennnet.com/Search/ShowIssue.cfm?Section=Search&ISSUE_NUM=4&VOLUME_NUM=14&ISSUE_DATE=]

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Hussman

#5186

solder balls | 8 February, 2001

OK, without knowing the specifics, why does everyone blame the oven? Most solder balls occur around R's and C's in almost every shop I've been to. The best place to start looking is the screen printer - not the oven. Sure the oven is the last process before the balling occurs, but doesn't mean it's the soul contributor to the balling.

Most solder balls that occur around R's and C's is due to too much paste being squeezed under the part during placement. The best cure for this is less paste. Yup, I said less paste, but less paste under the part when it's placed. Now before someone wings out a formula designed to slap some sense into me (or at least designed to make them look smart), I suggest using the homeplate design to accomplish this task of placing less paste. The "points of the homeplate point towards each other and are covered when the part is placed. Now when the part is placed, less paste is squished under the part and doesn't ball out towards the side of the part during reflow. You should get a proper solder joint and no balling. Most stencil houses have a general homeplate they use and should be enough to get ya through. If your using hot air solder leveled boards, you might want to reduce the over all pad by 10% and use the homeplate design.

Give it a try. all it costs is a stencil for a couple hundred bucks. If you don't like it, send it back for a refund and use your old stencil and use the formula someone is bound to post after this.

I guess I just should've said "Check the archives!", oh well......good luck!

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pr

#5187

solder balls | 8 February, 2001

You oven guys are SOOOO sensitive! I must agree though, the oven profile made nowhere near the difference that the Homeplate did, in our place.

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#5190

solder balls | 8 February, 2001

After reading the variety of responses, I feel moved to ask if you're you talking about what are occasionally referred to as solder beads (mid-chip solder balls, attached to the waste line of your chip caps and resistors) or the solder balls that tend to be more randomly scattered (as in spattered)?

The former is more paste volume related, the latter tends to be more profile and/or moisture related. At least that is my understanding, as I've never experienced it to any degree.

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Antonio

#5192

solder balls | 8 February, 2001

I wasn't specific which type. But all this info helps. Thanks a bunch fellas...

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SMT in-printer dispensing

reflow oven profiler