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Solder Balls

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We have been getting solder balls on some of our SMT boards ... - Apr 15, 2002 by

Search the fine SMTnet Archives to get started, until the So... - Apr 15, 2002 by davef

If the solder balls are next to your discretes, you should c... - Apr 19, 2002 by jnunns

Chances are your profile is fine. There is probably too much... - Apr 22, 2002 by

shawn, define what you mean by solder ball's scattered ac... - Apr 30, 2002 by JohnW

I'd tend to agree with what the others have said. Check the ... - May 09, 2002 by brian o

From your stencil, if not clean, you can have residues, try ... - May 19, 2002 by

Excess slump of paste and mis-registration can cause solde... - May 20, 2002 by

Shawn

#19515

Solder Balls | 15 April, 2002

We have been getting solder balls on some of our SMT boards that are scattered across the board. We are using AIMS RMA291 in a cartridge. The profile we run matches what is called out on the tech data sheet for the solder with only the soak time maybe being a little short. It calls out for 60 to 90 seconds and ours is a little under the minimum. One suggestion was moisture in the paste but if it isn't that what other possibilities are there?

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davef

#19517

Solder Balls | 15 April, 2002

Search the fine SMTnet Archives to get started, until the Solder Ball Troops arrive.

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jnunns

#19584

Solder Balls | 19 April, 2002

If the solder balls are next to your discretes, you should consider a homeplate design on you stencil apertures. THe only other time we have seen soler balls is due to the raw card. If the vias are not plugged by the solder mask, solder and air can get in the holes. Then during reflow, the temp creates a pressure that can drive the paste out. If the balls are sitting all over the place, but on vias, this may be your problem

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Steve Townsend

#19631

Solder Balls | 22 April, 2002

Chances are your profile is fine. There is probably too much paste on the descrete pads.

Consider reducing the aperture size of the stencil.

Good luck.

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Bob Willis

#19711

Solder Balls | 29 April, 2002

Had a similar problem recently where there were scatered balls and voids in joints and on the surface of the joints.

The paste was dispenced from a cartridge with no kneeding or mixing before printing. The result was spitting and voids. Mixed the paste or run a few pre prints eliminated the problem.

Bob Willis

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JohnW

#19737

Solder Balls | 30 April, 2002

shawn,

define what you mean by solder ball's scattered across the board? I'd tend to agree with the thoughts of too much paste on chip's but normally your ball's would be mainly around these devices although som can move around depending on the surface finish of the PCB - gloss Vs Matt and also the via pattern. Never worked with Aim paste so I don't know the charachteristic's but Bob's suggestion of movignt he paste in the cartridge sounds good, a very simple way of either discounting or solving it. Have any scatter graph's been done? although some ball's will find their way to area's of the PCB totally unrelated the high percentage will be in and around a specific problem area where thing's like excess paste would be highlighted. Other things to check are PCB to stencil gasket PCB finish - if it's HASL are your pad's nice n flat or really domed? Under stencil wiping - how regular is this gettign done, is it wet/dry/vac? Has the understencil wiper been set up correctly / is the paper clean? how are the board supports? basically check all your set up first, cross out these then move to the harder stuff of looking at your stencil and the cartridge.

John

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brian o

#19837

Solder Balls | 9 May, 2002

I'd tend to agree with what the others have said. Check the basics, board supports, setup, wiper paper working correctly. If it's a humidity issue, try taking some paste, place it on a chem wipe, and roll it around a bit, which removes some of the moisture (but the downside is it also removes flux) Knead the paste on 1-2 boards prior to printing a run board, and if these don't help, then you might have to reduce the size of the apetures, or maybe use a step down on those areas.

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#19977

Solder Balls | 19 May, 2002

From your stencil, if not clean, you can have residues, try increasing the frequency or using solvent with the wipe.

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Gary

#19984

Solder Balls | 20 May, 2002

Excess slump of paste and mis-registration can cause solder balls along with moisture. Use same date code of pcb and run with no components, paste only. Also pre-bake boards with humidity sensor in oven. If high humidity, moisture and solvent residues in via's a possibility.

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