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No-clean stencil apertures

James Graves

#9961

No-clean stencil apertures | 24 August, 1999

Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case).

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JohnW

#9962

Re: No-clean stencil apertures | 25 August, 1999

| Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | James,

Most decent paste vendor's will give you ratio's for your appetures and in part it depend's on the paste that you are using for the job. Typically I'm running a 6 thou stencil with a std 4 thou global reduction on all part's and 2 thou on fin pitch ( 20 thou and below) no solderball's and no dry's. The type of stencil is also important at the moment I'm using laser cut, it's not bad but I don't know if I'm completey sold on it yet but it seem's to be doing the job. One of the thing's to be careful of when your doing this is the screen must be kept clean, so I generally have a dry / wet wipe after a max of 10 boards sometimes less depending on the pitches.

hope this helps

JohnW

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Earl Moon

#9963

Re: No-clean stencil apertures | 25 August, 1999

| | Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | | | James, | | Most decent paste vendor's will give you ratio's for your appetures and in part it depend's on the paste that you are using for the job. | Typically I'm running a 6 thou stencil with a std 4 thou global reduction on all part's and 2 thou on fin pitch ( 20 thou and below) no solderball's and no dry's. | The type of stencil is also important at the moment I'm using laser cut, it's not bad but I don't know if I'm completey sold on it yet but it seem's to be doing the job. | One of the thing's to be careful of when your doing this is the screen must be kept clean, so I generally have a dry / wet wipe after a max of 10 boards sometimes less depending on the pitches. | | hope this helps | | JohnW | I'll buy that though I'm still using 6 mil trap etched stencils with downsized pads with nearly 1:1 apertures. Cleaning is most important with wet/vac/dry after every 3 panels. So many options, so little time.

Earl Moon

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#9964

Re: No-clean stencil apertures | 25 August, 1999

| Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | James: Sorry I don't get it. If the metal content of a no-clean paste is the same as the meetal content for a clean paste, why would the aperture be different? Solder volume is solder volume.

Now, when thinking about solder balls if all that's changed is the paste:

1 If you control your no-clean soldering process the same as you controlled your clean soldering process, you surely will have more balls. 2 Solder balls in a clean process give less aggravation than solder balls developed durinng a no-clean process, because those 'lil buggers get washed from the board.

My2�

Dave F

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Jason Tomlinson

#9965

Re: No-clean stencil apertures | 25 August, 1999

| Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | You also might want to measure your pads. I've had a lot trouble with over etched pads on the PCB's, which can nullify any aperture reductions on your stencil.

JT

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#9966

Re: No-clean stencil apertures | 26 August, 1999

| | | Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | | | | | James, | | | | Most decent paste vendor's will give you ratio's for your appetures and in part it depend's on the paste that you are using for the job. | | Typically I'm running a 6 thou stencil with a std 4 thou global reduction on all part's and 2 thou on fin pitch ( 20 thou and below) no solderball's and no dry's. | | The type of stencil is also important at the moment I'm using laser cut, it's not bad but I don't know if I'm completey sold on it yet but it seem's to be doing the job. | | One of the thing's to be careful of when your doing this is the screen must be kept clean, so I generally have a dry / wet wipe after a max of 10 boards sometimes less depending on the pitches. | | | | hope this helps | | | | JohnW | | | I'll buy that though I'm still using 6 mil trap etched stencils with downsized pads with nearly 1:1 apertures. Cleaning is most important with wet/vac/dry after every 3 panels. So many options, so little time. | | Earl Moon | It�s the same old story, pastes and printing. Now having designed our pads over and over to meet almost "any" requirement (space, supplier capabilities, tolerances of any kind, fillet considerations, reworkability ...) we ended up with 0.150mm lasercut and an overall aperture reduction of 15% and there aren�t any problems as long as printing is done correct, no balls, no opens. Still have some problems with boards done by subcons who use their own stencil design and the problem is usually solved by providing them with our stencils. Sounds like it�s only the printing but most work we put in redesign of landpatterns. Depending on the occurence of the balls, I think of chip-components, there was this thread a few weeks ago about arrowshaped apertures, I found it quite interesting.

I asked for wisdom and I was given problems to solve, so I got everything I needed.

Wolfgang

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swsng

#9967

Re: No-clean stencil apertures | 27 August, 1999

| Does anyone have any information on stencil aperture/pad ratios for noclean solder paste. In the past I have experienced severe solder ball problems when using the same size apertures from aqueous products as I do with the No-clean products. Consequently, a reduced sized aperture for for No-clean assemblies tend to have more open (in our case). | a REDUCTION OF OPENING.APPROX.85 TO 95 % OF THE ACTUAL PADS AND THE DIFFERENCE BETWEEN BOTH RATIO MUST BE >1.5 FATOR FOR 20MILS QFP REDUCE 2 MILS HEEL AND INCREASE 2MIL AT TOES AT SIDES -1MILS EACH. SWSNG

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