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Flux dip or solder print for CSP

Views: 1651

#76961

Flux dip or solder print for CSP | 30 January, 2017

Hi all,

I'm wondering how does one decide to use flux dipping or solder printing when it comes to be attaching CSPs onto the board?

Solder printing has an advantage in that there will be a higher throughput on the mounter as there is no flux dipping motion needed but I'm sure there is some sort of limitation there.

Any comments?

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Rob

#76975

Flux dip or solder print for CSP | 31 January, 2017

Hi Joshua,

We've done both, but a lot depends on what soloution your machine vendor has, and how good it is.

Can you add it into your machine acceptance criteria?

Rob.

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#76976

Flux dip or solder print for CSP | 31 January, 2017

If there is no specific quality reason, stay with paste. More processes you add, more points of failure. They don't need a lot of paste to get attached to the board. The ones I used were 8mil round apertures, so I did cut 1:1 on a 3 mil coated stencil and it worked perfect. For repair you can use the tacky flux only

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#76984

Flux dip or solder print for CSP | 31 January, 2017

I have solder bumps diameters @ 80um, the board pad size @ 100um.

Can this size be printed? How about dispensing?

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Rob

#76990

Flux dip or solder print for CSP | 1 February, 2017

80 micrometres (0.08mm) or 80 mil (2mm)?

Smallest I've seen reliably printed is around 0.2mm x 0.4mm (01005 pad) and 0.2mm x 0.2mm CSP pad, not seen anything dispensed below 0.35ish, but we are not cutting edge.

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#76992

Flux dip or solder print for CSP | 1 February, 2017

80 micrometres (0.08mm)

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Rob

#76994

Flux dip or solder print for CSP | 1 February, 2017

Ok, that's small - I think you may need a special semi-conductor printer for this - positional accuracy on a "normal" SMT printer is no more than 20 micrometres from memory.

In my semiconductror fab days we were printing with a positional accuracy of 10 micrometres, but this was extremely expensive kit.

Also, the paste particle size is going to be a huge factor - at this size you may be looking at silver epoxy.

Over to Guru Dave I think....

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#77000

Flux dip or solder print for CSP | 1 February, 2017

Joshua,

100um is 4mil aperture. You should ask several stencil houses about the possibility to print that small amount of paste(type 6 paste is available now with very small solder spheres 5-15um diameter). Even applying small amount(thin layer of flux might be very challenging too. If I was you I would be tempted to research other ways as well. i remember seeing a conductive adhesive tape(very thin tape) and other things ....this one is very interesting...please keep us posted

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#77091

Flux dip or solder print for CSP | 13 February, 2017

Solder flux and solder paste deposition is a standard step during the chip attach and sphere attach portions of BGA and CSP assembly. A technique called ultra-violet fluorescence intensity mapping (UV FIM) has been introduced that allows flux measurement for system set up, process characterization and production process control. This UV FIM technique can also be used for solder paste inspection and is faster than most existing technologies for this application.

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