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Solder paste print with two thicknesses

Thomas Blesinger

#13947

Solder paste print with two thicknesses | 7 October, 1998

I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. Thanks for help. Regards Thomas

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Charles Stringer

#13948

Re: Solder paste print with two thicknesses | 7 October, 1998

| I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | Thanks for help. | Regards Thomas | | You can use a stepped screen i.e. different foil thickneses in different areas however you wil require a separation between the thin and thick parts of your pattern. Alternatively try printing the same thickness everywhere and use a solder preform where you require the additional thickness

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Dave F

#13949

Re: Solder paste print with two thicknesses | 7 October, 1998

| I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | Thanks for help. | Regards Thomas | | Thomas: A stepped stencils that Charles mentioned is a great approach for many applications. An alternative to consider is using two stencils of different thicknesses. Print using the thin, standard stencil first. Print with the thicker stencil after the thinner stencil. The thick stencil should be stepped, like Charles mentioned, but the steps:

1. Are on the side of the foil that touches the board. 2. Correspond to the areas that received the thin paste deposit.

TTYL

Dave F

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MMurphy

#13950

Re: Solder paste print with two thicknesses | 7 October, 1998

| I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | Thanks for help. | Regards Thomas | | A "Stepped Down" stencil is the answer. You would start with a 250 micron (10mil) foil and etch down the 85% area to 120 microns (~5mil). This is a fairly aggressive step but it can be done . You would need at least a 200-300 mil "buffer" between the step and the closest apertures. Also, a relatively soft (~60-70D) poly blade would be required for printing. Call 1-800-748-2033 and ask for Cstmr Svc. for more info.

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Joe P.

#13951

Re: Solder paste print with two thicknesses | 7 October, 1998

| | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | Thanks for help. | | Regards Thomas | | | Thomas, I agree with MMurphy, a step stencil is really your only answer, but this is a HUGE step, and may be very difficult to do. What is the reason for this additional paste? Is is a shield that you have to hold down, or maybe a connector of some sort? Or is is a coplanarity issue? There may be other ways to accomplish what you are doing without that large of a step.

-Joe | A "Stepped Down" stencil is the answer. You would start with a 250 micron (10mil) foil and etch down the 85% area to 120 microns (~5mil). This is a fairly aggressive step but it can be done . You would need at least a 200-300 mil "buffer" between the step and the closest apertures. Also, a relatively soft (~60-70D) poly blade would be required for printing. | Call 1-800-748-2033 and ask for Cstmr Svc. for more info. |

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Thomas Blesinger

#13952

Re: Solder paste print with two thicknesses | 8 October, 1998

| | | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | | Thanks for help. | | | Regards Thomas | | | | | Thomas, | I agree with MMurphy, a step stencil is really your only answer, but this is a HUGE step, and may be very difficult to do. What is the reason for this additional paste? Is is a shield that you have to hold down, or maybe a connector of some sort? Or is is a coplanarity issue? There may be other ways to accomplish what you are doing without that large of a step. | | -Joe Hello Joe, as you already mention, we have to accomplish this high solder paste amount of 250 microns in order to solder a connector. It is a fully SMD capable connector, no pin-through-paste thing. Our coplanarity is 100 microns. We have made soldering tests with 150, 200 and 250 microns. The results with 150 microns showed real problems, the 200 microns were ok. but some joints were a bit poor, although soldered. With 250 microns all was just fine. Do you have any idea on a solution. If you want, you can have samples of the connector. Thanks for your help. Regards Thomas

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Thomas Blesinger

#13953

Re: Solder paste print with two thicknesses | 8 October, 1998

| | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | Thanks for help. | | Regards Thomas | | | | | Thomas: A stepped stencils that Charles mentioned is a great approach for many applications. An alternative to consider is using two stencils of different thicknesses. Print using the thin, standard stencil first. Print with the thicker stencil after the thinner stencil. The thick stencil should be stepped, like Charles mentioned, but the steps: | | 1. Are on the side of the foil that touches the board. | 2. Correspond to the areas that received the thin paste deposit. | | TTYL | | Dave F | Hi Dave, that is a bit to complicated for me. Can you explain more in detail please. Do you mean to put a stepped stencil over the thin stencil, that is still on the board. The stepped Stencil would then have to be with holes only for the high pads. Don't you then have the risk of the already printed low pads sticking onto the backside of the stepped stencil? If you take that away then can't you tear away part of the solder depot of the low pads with it? Maybe I really didn't understand at all.

Regards Thomas

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JGodfrey

#13954

Re: Solder paste print with two thicknesses | 8 October, 1998

| I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | Thanks for help. | Regards Thomas | | Another method of attack is to look into a dispensing system like a Camalot. I've had very good luck dispensing solder paste, epoxy and condutive epoxy with them.

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Dave F

#13955

Re: Solder paste print with two thicknesses | 8 October, 1998

| | | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | | Thanks for help. | | | Regards Thomas | | | | | | | | Thomas: A stepped stencils that Charles mentioned is a great approach for many applications. An alternative to consider is using two stencils of different thicknesses. Print using the thin, standard stencil first. Print with the thicker stencil after the thinner stencil. The thick stencil should be stepped, like Charles mentioned, but the steps: | | | | 1. Are on the side of the foil that touches the board. | | 2. Correspond to the areas that received the thin paste deposit. | | | | TTYL | | | | Dave F | | | Hi Dave, | that is a bit to complicated for me. Can you explain more in detail please. Do you mean to put a stepped stencil over the thin stencil, that is still on the board. The stepped Stencil would then have to be with holes only for the high pads. Don't you then have the risk of the already printed low pads sticking onto the backside of the stepped stencil? If you take that away then can't you tear away part of the solder depot of the low pads with it? | Maybe I really didn't understand at all. | | Regards | Thomas | Thomas: Sorry I wasn't clear. Make two stencils:

1 Thin stencil with all aperatures except those that require the thick deposit 2 Thick stencil with only the aperatures that require a thick deposit. Cut a step(s) into the board side of the stencil that correspond to the area of the pads that require the thin paste deposition. Be generous about this area because both stencils will not be mounted in their frames exactly the same. The depth of the step should be greater than the thin stencil paste deposit.

Print paste in the following sequence:

1 Print with the thin stencil first 2 Remove thin stencil from the printer 3 Print with the thick stencil 4 Remove the thick stencil

TTYL

Dave F

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Dave F

#13956

Re: Solder paste print with two thicknesses | 8 October, 1998

| | | | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | | | Thanks for help. | | | | Regards Thomas | | | | | | | Thomas, | | I agree with MMurphy, a step stencil is really your only answer, but this is a HUGE step, and may be very difficult to do. What is the reason for this additional paste? Is is a shield that you have to hold down, or maybe a connector of some sort? Or is is a coplanarity issue? There may be other ways to accomplish what you are doing without that large of a step. | | | | -Joe | Hello Joe, | as you already mention, we have to accomplish this high solder paste amount of 250 microns in order to solder a connector. It is a fully SMD capable connector, no pin-through-paste thing. Our coplanarity is 100 microns. We have made soldering tests with 150, 200 and 250 microns. The results with 150 microns showed real problems, the 200 microns were ok. but some joints were a bit poor, although soldered. With 250 microns all was just fine. Do you have any idea on a solution. If you want, you can have samples of the connector. | Thanks for your help. | Regards | Thomas | Thomas: What shape and size are the aperatures to print paste for the connector? Can you do something like ...

1 Using a (250m + 120m)/2 or so thick foil? 2 Pinching the non-connector pads? 3 Increasing the aperatures for the connector beyond the pad size and maybe putting tear shaped additions on the ends of the connector aperatures to get the volume of paste you require?

TTYL

Dave F

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Thomas Blesinger

#13957

Re: Solder paste print with two thicknesses | 9 October, 1998

| Thomas: What shape and size are the aperatures to print paste for the connector? Can you do something like ... | | 1 Using a (250m + 120m)/2 or so thick foil? | 2 Pinching the non-connector pads? | 3 Increasing the aperatures for the connector beyond the pad size and maybe putting tear shaped additions on the ends of the connector aperatures to get the volume of paste you require? | | TTYL | | Dave F | Dave, thats seems to be a good idea to me. I will discuss this with my technicians. Thanks Thomas

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Thomas Blesinger

#13958

Re: Solder paste print with two thicknesses | 9 October, 1998

| | | | I am trying to find out, what possibilities I have, to print solder paste on a board, when the task is to have 120 Microns thickness for the biggest part of the board (85% of the real estate), and then have 250 Microns of thickness on the remaining part. This part usually will be a stripe along the edge of the board. | | | | Thanks for help. | | | | Regards Thomas | | | | | | | | | | | Thomas: A stepped stencils that Charles mentioned is a great approach for many applications. An alternative to consider is using two stencils of different thicknesses. Print using the thin, standard stencil first. Print with the thicker stencil after the thinner stencil. The thick stencil should be stepped, like Charles mentioned, but the steps: | | | | | | 1. Are on the side of the foil that touches the board. | | | 2. Correspond to the areas that received the thin paste deposit. | | | | | | TTYL | | | | | | Dave F | | | | | Hi Dave, | | that is a bit to complicated for me. Can you explain more in detail please. Do you mean to put a stepped stencil over the thin stencil, that is still on the board. The stepped Stencil would then have to be with holes only for the high pads. Don't you then have the risk of the already printed low pads sticking onto the backside of the stepped stencil? If you take that away then can't you tear away part of the solder depot of the low pads with it? | | Maybe I really didn't understand at all. | | | | Regards | | Thomas | | | Thomas: Sorry I wasn't clear. Make two stencils: | | 1 Thin stencil with all aperatures except those that require the thick deposit | 2 Thick stencil with only the aperatures that require a thick deposit. Cut a step(s) into the board side of the stencil that correspond to the area of the pads that require the thin paste deposition. Be generous about this area because both stencils will not be mounted in their frames exactly the same. The depth of the step should be greater than the thin stencil paste deposit. | | Print paste in the following sequence: | | 1 Print with the thin stencil first | 2 Remove thin stencil from the printer | 3 Print with the thick stencil | 4 Remove the thick stencil | | TTYL | | Dave F | Dave, O.K. got that now, will discuss, Thanks Thomas

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Sanjay Bhatikar

#13959

Re: Solder paste print with two thicknesses | 13 October, 1998

Sir,

I have been thinking about your problem. I have a suggestion that may work, although it has not been tried before.

How about using two stencils? First print the the whole board with a stencil for 150 micron thickness. Next, place a stencil etched with the pattern of 250 micron thickness. (This second stencil would be 100 micron thick, and located exactly on the stencil for the 1st stage by means of location pins.) Now, print again.

Do you want to give it a try? SMTneters! What do you think?

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Fraser

#13960

Re: Solder paste print with two thicknesses | 1 November, 2000

Thomas,

Dave is right - we had a similar coplanarity problem on some BGAs which we solved simply by over printing - no step required by nearly 2 x what happens is that the paste hight will grow as the paste reflows confined by the pad drop me line and I will explain.

cheers

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