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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Robert Meston

#16168

SMD mounting height | 17 April, 1998

We have to mount our SMD devices 0.1 to 0.4 mm off the pcb PCb substrate to compensate for thermal stressing in a Space enviroment. Has any one any ideas or contacts for dissolvable pads. this only applies to leadless components

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Justin Medernach

#16173

Re: SMD mounting height | 17 April, 1998

| We have to mount our SMD devices 0.1 to 0.4 mm off the pcb | PCb substrate to compensate for thermal stressing in a | Space enviroment. Has any one any ideas or contacts for | dissolvable pads. this only applies to leadless components Robert, Try that 3M double sided foam tape. It's about the thickness you're looking for. It's not disolvable but completely inert. Regards, Justin Medernach

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D.Lange

#16172

Re: SMD mounting height | 19 April, 1998

| We have to mount our SMD devices 0.1 to 0.4 mm off the pcb | PCb substrate to compensate for thermal stressing in a | Space enviroment. Has any one any ideas or contacts for | dissolvable pads. this only applies to leadless components Robert, PPI Adhesives Products group as well as 3M manufacture water soluable masking tape which can be die cut (Saunders) to your specifications. Designed for wave solder masking however may work for your application. Thicness is .055MM +/-.008 using two die cut dots may just the height you need (.110 MM). Tape readily disolves with 150 (F) degree water. Tape can withstand 260 (C) degrees for about 25 seconds. Should be no problem at reflow temp assuming good profile.

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D.Lange

#16170

Re: SMD mounting height | 19 April, 1998

| We have to mount our SMD devices 0.1 to 0.4 mm off the pcb | PCb substrate to compensate for thermal stressing in a | Space enviroment. Has any one any ideas or contacts for | dissolvable pads. this only applies to leadless components Robert, PPI Adhesives Products (610)251-9834 group as well as 3M manufacture water soluable masking tape which can be die cut (Saunders) to your specifications. Designed for wave solder masking however may work for your application. Thickness is .055MM +/-.008 using two die cut dots may just the height you need (.110 MM). Tape readily disolves with 150 (F) degree water. Tape can withstand 260 (C) degrees for about 25 seconds. Should be no problem at reflow temp assuming good profile. E-mail if you like have data sheets... if you need more info. Good Luck!

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Stan Traxler

#16169

Re: SMD mounting height | 25 April, 1998

| We have to mount our SMD devices 0.1 to 0.4 mm off the pcb | PCb substrate to compensate for thermal stressing in a | Space enviroment. Has any one any ideas or contacts for | dissolvable pads. this only applies to leadless components We have applications in our facility in which we glue our components, (not only chips but also LCC's to pwa's) for wave solder. Within this process we: Stencil solder on the pads of the pwa, dispense glue for the components, place the components, then reflow the solder. When we do this the resulting component is spaced up off the pwa the height that it was depressed into the paste by the pick and place (varies by placement pressure). This happens because the glue cures prior to the solder reflowing, which does not allow the component to "settle" down to the pwa the way it normally would during reflow. I've never measured the resulting standoff of the component from the pwa, or it's repeatability, but depending on stencil thickness I'm sure you would get .1mm (.0039"). If you have an auto adhesive dispenser, this could be a very repeatable process. I think this method would work better than the dissolvable pad method because preapplying the pads before stencil printing would make printed difficult and applying them after stencil printing could lead to smudging your prints.

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Chrys

#16171

Re: SMD mounting height | 28 April, 1998

| | We have to mount our SMD devices 0.1 to 0.4 mm off the pcb | | PCb substrate to compensate for thermal stressing in a | | Space enviroment. Has any one any ideas or contacts for | | dissolvable pads. this only applies to leadless components | Robert, | PPI Adhesives Products (610)251-9834 group as well as 3M manufacture water soluable masking tape which can be die cut (Saunders) to your specifications. Designed for wave solder masking however may work for your application. Thickness is .055MM +/-.008 using two die cut dots may just the height you need (.110 MM). Tape readily disolves with 150 (F) degree water. Tape can withstand 260 (C) degrees for about 25 seconds. Should be no problem at reflow temp assuming good profile. E-mail if you like have data sheets... if you need more info. Good Luck! I've used the water soluble die cut tapes and they work really well - no residue. But you have to place them by hand. I know of a company that specializes in feeder systems for all kinds of crazy SMT stuff. They can do flexible tapes, labels, etc. E-mial if you want the info. Chrys

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HeatShield Gel- thermal PCB shield during reflow

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