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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Jason Gregory

#10208

Strange problem with my dispenser | 10 August, 1999

Has anyone ever heard of this? I have a Camalot System 5000 and we were in a pinch to produce some prototype boards. We needed Sn62Pb36Ag2-no clean in a dispensing mesh. All I could get my hands on was some Interflux paste in a jar. The formulation is correct and the mesh is 325/500 (stencil printing mesh, not dispensing). I figured the only bad thing that would happen is the paste would not flow as easily through the nozzle, due to the ball size. Instead I found that the flow stopped, as if obstructed. I dissambled the pump and found a chunk of solder that appeared like flowed solder. Shiny and hard like a solder joint and I pushed it out. The pump on the Camalot is an Archimedes-style one and I'm guessing that the pump compressed the balls, because of their large size and their resistance to flow through the small hole, into a clump, causing the obstruction. But why does the clump appeared soldered. Now, I know there is no heat in the pump to cause the solder to "flow", so what the hee-haw is happening here? Any suggestions??? Too weird!!!!

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Brian

#10209

Re: Strange problem with my dispenser | 11 August, 1999

| Has anyone ever heard of this? I have a Camalot System 5000 and we were in a pinch to produce some prototype boards. We needed Sn62Pb36Ag2-no clean in a dispensing mesh. All I could get my hands on was some Interflux paste in a jar. The formulation is correct and the mesh is 325/500 (stencil printing mesh, not dispensing). I figured the only bad thing that would happen is the paste would not flow as easily through the nozzle, due to the ball size. Instead I found that the flow stopped, as if obstructed. I dissambled the pump and found a chunk of solder that appeared like flowed solder. Shiny and hard like a solder joint and I pushed it out. The pump on the Camalot is an Archimedes-style one and I'm guessing that the pump compressed the balls, because of their large size and their resistance to flow through the small hole, into a clump, causing the obstruction. But why does the clump appeared soldered. Now, I know there is no heat in the pump to cause the solder to "flow", so what the hee-haw is happening here? Any suggestions??? Too weird!!!! | Many years ago, I had a Swiss watchmaker customer who was hand-dispensing a fine-powder paste (I forget the details), using about 5 g of paste per syringe and a 25 G needle (which was far too small). After air-dispensing about half the paste, with a well lubricated rubber piston and virtually no air under it, he would need to change both syringe and needle. Each shot had about 5-8 grains of powder! On microscopic examination of the paste left in the syringe, we found clumping of two or three powder grains fairly frequently, which we thought was due to the constant compression/decompression as each air pulse passed. We also examined the needles very carefully and found that a few of them contained a sintered mass of powder particles of about 0.2-0.3 mm across, which get polished as other particles pass by. Cross sectioning them revealed a true cold fusion where the particles were pressed (or, rather, hammered) together, presumably with the chemistry squeezed out. We did three x-sections of these, one contained a chemistry-filled void, the other two solid metal. The crystal structure defined no boundary within the particles.

I recount this because your story has a certain resemblance. I don't know whether the relevance is perfect.

Brian

PS It was good business for us while it lasted: we filled about 500 syringes per week for them for about 3 or 4 years! Then they went bankrupt, maybe because we insisted cash-on-delivery!

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#10210

Re: Strange problem with my dispenser | 11 August, 1999

| | Has anyone ever heard of this? I have a Camalot System 5000 and we were in a pinch to produce some prototype boards. We needed Sn62Pb36Ag2-no clean in a dispensing mesh. All I could get my hands on was some Interflux paste in a jar. The formulation is correct and the mesh is 325/500 (stencil printing mesh, not dispensing). I figured the only bad thing that would happen is the paste would not flow as easily through the nozzle, due to the ball size. Instead I found that the flow stopped, as if obstructed. I dissambled the pump and found a chunk of solder that appeared like flowed solder. Shiny and hard like a solder joint and I pushed it out. The pump on the Camalot is an Archimedes-style one and I'm guessing that the pump compressed the balls, because of their large size and their resistance to flow through the small hole, into a clump, causing the obstruction. But why does the clump appeared soldered. Now, I know there is no heat in the pump to cause the solder to "flow", so what the hee-haw is happening here? Any suggestions??? Too weird!!!! | | | Many years ago, I had a Swiss watchmaker customer who was hand-dispensing a fine-powder paste (I forget the details), using about 5 g of paste per syringe and a 25 G needle (which was far too small). After air-dispensing about half the paste, with a well lubricated rubber piston and virtually no air under it, he would need to change both syringe and needle. Each shot had about 5-8 grains of powder! On microscopic examination of the paste left in the syringe, we found clumping of two or three powder grains fairly frequently, which we thought was due to the constant compression/decompression as each air pulse passed. We also examined the needles very carefully and found that a few of them contained a sintered mass of powder particles of about 0.2-0.3 mm across, which get polished as other particles pass by. Cross sectioning them revealed a true cold fusion where the particles were pressed (or, rather, hammered) together, presumably with the chemistry squeezed out. We did three x-sections of these, one contained a chemistry-filled void, the other two solid metal. The crystal structure defined no boundary within the particles. | | I recount this because your story has a certain resemblance. I don't know whether the relevance is perfect. | | Brian | | PS It was good business for us while it lasted: we filled about 500 syringes per week for them for about 3 or 4 years! Then they went bankrupt, maybe because we insisted cash-on-delivery! | Brian's correct. The solder balling caused by adiabatic compression heating of the materials in the syringe. To prevent this problem:

* Reduce the dispenser pressure. * Reduce the surrounding temperature in the dispensing machine with air conditioning. * Increase the needle size. * Use a finer mesh solder paste.

My2�

Dave F

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