I etched PCBs, as a juvenile. As a rental apartment dwelling geezer, PCB etching is not going to happen.
Still all the techniques and info. provided are highly appreciated. The idea of using "FunTak" as an extra hand is particularly appealing. That idea could be incorporated into developing a method for soldering pigtails onto SMD parts. Low melting point 63/37 Sn/Pb eutectic is still legal in the U.S.A. and seems to be an obvious alloy choice.
I haven't given up on the conductive cement idea.
One poster expressed concern about conductivity. I extracted "Good 0.017 Ω·cm electrical resistivity and 0.90 W/(m·K) thermal conductivity" from the product info. sheet. That appears quite good to me. I am concerned about the high price and 2 year shelf life.
Still all the techniques and info. provided are highly appreciated. The idea of using "FunTak" as an extra hand is particularly appealing. That idea could be incorporated into developing a method for soldering pigtails onto SMD parts. Low melting point 63/37 Sn/Pb eutectic is still legal in the U.S.A. and seems to be an obvious alloy choice.
I haven't given up on the conductive cement idea.
One poster expressed concern about conductivity. I extracted "Good 0.017 Ω·cm electrical resistivity and 0.90 W/(m·K) thermal conductivity" from the product info. sheet. That appears quite good to me. I am concerned about the high price and 2 year shelf life.I use SMD parts all the time, using a countertop toaster oven. Inexpensive, low powered ones are the best. Avoid the expensive, high powered ones, they heat of too fast and have too many features that will get in the way. At Walmart or Target, budget $25 or so – much less than a good soldering iron! An inexpensive oven will heat up more slowly and give the proper thermal profile for doing SMD soldering.
Please, DO NOT use the toaster oven in your kitchen. Your spouse will not be amused and once the oven is used for soldering, it will no longer be fit for food preparation. You will want to use this in a well-ventilated, well-lit location. When you heat up solder paste, the fumes can concentrate and make you dizzy – take my word on this!
Solder paste is available in many grades and styles. Look for one that is water washable. This will allow you to clean off the residue easily. It typically comes in small amounts in syringes. It is best to refrigerate the paste, this makes it last longer. The paste comes with a limited shelf life – 6 months or so, but I have successfully used paste that is a few years beyond the stated shelf life.
There are two methods of applying solder paste to the board. If you are doing one or two boards, applying paste by hand is a reasonable approach. For larger numbers of boards, purchasing a stencil is by far the preferred method.
To apply paste by hand, use a toothpick to apply a dot of solder paste to each pad. You do not need or want to cover the entire pad with paste, just enough so that the component will have a sufficient amount to adhere to the board. If in doubt, use slightly less than you would think is necessary.
To use a stencil, first you must have a stencil made. Many board manufacturers also produce stencils. You will need a gerber file of the board that includes the dimension layer and the tCream layer. This is then sent to the manufacturer who will provide a stainless steel stencil which has cutouts for each solder pad. Align the stencil over the board then apply a bead of solder paste at one end. Use the provided piece of stainless to wipe the solder across the board. Paste will be applied to the board in an even layer over the entire pad in the thickness of the stencil. Carefully remove the stencil and you will have a board with the solder paste applied.
To place the parts, it is very helpful to have an illuminated magnifying glass and a good set of tweezers. Some of the parts are small, and almost impossible to pick up using your fingers. Even if you were able to pick up the part with your fingers, you would most likely smear the paste on adjacent pads when placing the part. Try to align the parts carefully. Where you place the parts is where they will end up, except in two cases:
If you put too much solder on the pad, the part may float up, then float off of the pad during solder flow. In the case of an IC, the surface tension of the solder will help to align the part to the pads even if the part is slightly mis-aligned. If there is too much solder, however, the part may self-align to adjacent pads, a difficult repair.
Once the parts have all been placed on the board, it is time to bake the boards.
Start with a cold oven. Place the board in the center of the oven and close the door. Set the controls to “Bake” and “Always On” if you have those settings. We want to use manual timing and not use the self-timer functions on the oven. Set the temperature control to 200 deg F then turn on the oven. We want to bake at 200 deg for 4 minutes. This will help equalize all of the parts and the board to a low working temperature. Going to this low temperatire will prevent a large shock to the parts and keep parts from breaking due to the shock.
After the 4 minute soak, increase the temperature to 325 deg F. We will leave the temperature setting here for 2 additonal minutes. This next temperature level will allow any moisture to evaporate and let all the parts get to a steady state that is below the melting point of the solder.
At the end of this 2 minute soak, increase the temperature one last time to 450 deg F. This is higher than the melting point of solder. Watch the board closely. After about a minute, you should see the paste start to melt and turn shiny. Keep the oven on for 30 seconds after all the solder has melted. Then turn opff the oven and open the oven door. Opening the door will shake the board slightly. This will help the ICs to settle into position. Leave the door open until the board cools enough to touch, which is usually about 15 minutes. Do not rush this portion - the solder may still be partially pliable and parts could be shocked loose.
After cooling, inspect the board to solder balls and bridges, and check to see if any parts have floated away from the pads. This can usually be fixed with a fine-tip iron. Solder bridges can be removed with a piece of solder wick.
If you make an error on the timing of the process, allow a longer soak at 200 deg and 325 deg rather than shortening these times. Time the final 30 seconds closely. Too long at 450 deg can damage the parts.
Please, DO NOT use the toaster oven in your kitchen. Your spouse will not be amused and once the oven is used for soldering, it will no longer be fit for food preparation. You will want to use this in a well-ventilated, well-lit location. When you heat up solder paste, the fumes can concentrate and make you dizzy – take my word on this!
Solder paste is available in many grades and styles. Look for one that is water washable. This will allow you to clean off the residue easily. It typically comes in small amounts in syringes. It is best to refrigerate the paste, this makes it last longer. The paste comes with a limited shelf life – 6 months or so, but I have successfully used paste that is a few years beyond the stated shelf life.
There are two methods of applying solder paste to the board. If you are doing one or two boards, applying paste by hand is a reasonable approach. For larger numbers of boards, purchasing a stencil is by far the preferred method.
To apply paste by hand, use a toothpick to apply a dot of solder paste to each pad. You do not need or want to cover the entire pad with paste, just enough so that the component will have a sufficient amount to adhere to the board. If in doubt, use slightly less than you would think is necessary.
To use a stencil, first you must have a stencil made. Many board manufacturers also produce stencils. You will need a gerber file of the board that includes the dimension layer and the tCream layer. This is then sent to the manufacturer who will provide a stainless steel stencil which has cutouts for each solder pad. Align the stencil over the board then apply a bead of solder paste at one end. Use the provided piece of stainless to wipe the solder across the board. Paste will be applied to the board in an even layer over the entire pad in the thickness of the stencil. Carefully remove the stencil and you will have a board with the solder paste applied.
To place the parts, it is very helpful to have an illuminated magnifying glass and a good set of tweezers. Some of the parts are small, and almost impossible to pick up using your fingers. Even if you were able to pick up the part with your fingers, you would most likely smear the paste on adjacent pads when placing the part. Try to align the parts carefully. Where you place the parts is where they will end up, except in two cases:
If you put too much solder on the pad, the part may float up, then float off of the pad during solder flow. In the case of an IC, the surface tension of the solder will help to align the part to the pads even if the part is slightly mis-aligned. If there is too much solder, however, the part may self-align to adjacent pads, a difficult repair.
Once the parts have all been placed on the board, it is time to bake the boards.
Start with a cold oven. Place the board in the center of the oven and close the door. Set the controls to “Bake” and “Always On” if you have those settings. We want to use manual timing and not use the self-timer functions on the oven. Set the temperature control to 200 deg F then turn on the oven. We want to bake at 200 deg for 4 minutes. This will help equalize all of the parts and the board to a low working temperature. Going to this low temperatire will prevent a large shock to the parts and keep parts from breaking due to the shock.
After the 4 minute soak, increase the temperature to 325 deg F. We will leave the temperature setting here for 2 additonal minutes. This next temperature level will allow any moisture to evaporate and let all the parts get to a steady state that is below the melting point of the solder.
At the end of this 2 minute soak, increase the temperature one last time to 450 deg F. This is higher than the melting point of solder. Watch the board closely. After about a minute, you should see the paste start to melt and turn shiny. Keep the oven on for 30 seconds after all the solder has melted. Then turn opff the oven and open the oven door. Opening the door will shake the board slightly. This will help the ICs to settle into position. Leave the door open until the board cools enough to touch, which is usually about 15 minutes. Do not rush this portion - the solder may still be partially pliable and parts could be shocked loose.
After cooling, inspect the board to solder balls and bridges, and check to see if any parts have floated away from the pads. This can usually be fixed with a fine-tip iron. Solder bridges can be removed with a piece of solder wick.
If you make an error on the timing of the process, allow a longer soak at 200 deg and 325 deg rather than shortening these times. Time the final 30 seconds closely. Too long at 450 deg can damage the parts.
For reflow you can add a controller, a thermocouple and an SSR to get a PID controlled reflow process on a cheap oven.
See here for an example done with an arduino that can be done relatively cheaply - http://www.rocketscream.com/wiki/index.php/Reflow_Controller_Shield_(Arduino_Compatible)
I haven't actually tried the manual timing process but I have an oven half pulled apart waiting for me to install the relay 😎
I do not understand the preference for P2P over PCB construction methods especially now that PCBs can be produced quickly and cheaply.
See here for an example done with an arduino that can be done relatively cheaply - http://www.rocketscream.com/wiki/index.php/Reflow_Controller_Shield_(Arduino_Compatible)
I haven't actually tried the manual timing process but I have an oven half pulled apart waiting for me to install the relay 😎
I do not understand the preference for P2P over PCB construction methods especially now that PCBs can be produced quickly and cheaply.
Safe preparation of PCBs by a rental apartment dweller, like yours truly, is anything but easy or inexpensive.
High quality "vintage" equipment undergoing refurbishment is P2P and staying that way. However, if a SMD part of superior characteristics is available, it would be nice to be able to conveniently employ it in a rebuild project.
PCBs are inherently 2 dimensional things. Space saving and (sometimes) performance improving 3 dimensional wiring is available, when P2P is employed.
Neither P2P nor PCB is fundamentally superior. Execution details are the key to highly satisfactory results, when either method is employed. Yes, it's perfectly acceptable to employ PCBs and P2P, in combination, to achieve a specific, high quality, result. Once again, a "single size", definitely, does not fit all.
SMDs are simply a different package for the same die (the actual semiconductor circuit inside the epoxy package. The package and its legs are simply shrunk down.
The main disadvantage of SMDs is working with the much smaller lead pitches (the distances between the pins or legs). Good soldering techniques are more important when using SMDs than through-hole parts due to the smaller pitch.
I've pretty much resigned myself to the fact that through-hole components are a dying commodity. So pretty much anything I design commercially uses SMD. If you're building more than a few, it's also easier to get SMD stuff assembled.
I also routinely do toaster-oven reflow for prototypes. With a microscope, even 0402 parts are possible even for an old guy like me 🙂 You can buy a real solder stencil kit for less than $100 these days, from places like SMT Stencils - Prototype Stencil Kits - Surface Mount Technology Stencil from QuickStencil - SMT - Surface Mount Tools - $ 89-$99 Prototype Stencil Kit - Fixed Frame Stencils - $99 Plate/Foil Only Stencils.
But to the point of the original post...
For ICs, you can buy adapter boards that let you put SMD IC's down on, for example a perfboard. Like these: Invalid Request (the link should work...)
However, for smaller parts and passives, I don't think anything like this exists.
Of course, I've thought about making some. I'm just not sure that there are any needs that are common enough to justify designing and building boards.
I was toying with doing an active bridge rectifier board ("lossless" bridge using MOSFETS). It might be nice for DC filaments and heaters, especially when you want to generate something like 5VDC from 5VAC...
Pete
I also routinely do toaster-oven reflow for prototypes. With a microscope, even 0402 parts are possible even for an old guy like me 🙂 You can buy a real solder stencil kit for less than $100 these days, from places like SMT Stencils - Prototype Stencil Kits - Surface Mount Technology Stencil from QuickStencil - SMT - Surface Mount Tools - $ 89-$99 Prototype Stencil Kit - Fixed Frame Stencils - $99 Plate/Foil Only Stencils.
But to the point of the original post...
For ICs, you can buy adapter boards that let you put SMD IC's down on, for example a perfboard. Like these: Invalid Request (the link should work...)
However, for smaller parts and passives, I don't think anything like this exists.
Of course, I've thought about making some. I'm just not sure that there are any needs that are common enough to justify designing and building boards.
I was toying with doing an active bridge rectifier board ("lossless" bridge using MOSFETS). It might be nice for DC filaments and heaters, especially when you want to generate something like 5VDC from 5VAC...
Pete
SMD resistors seem not to be a problem.
But there seems to be a belief, an idea or probably a preconception, that there are no SMD electrolytics that may sound well.
Until someone gives me some reasonable and objective explanation for that, I think there are SMD electrolytics that may sound good.
Someone made any comparisons?
But there seems to be a belief, an idea or probably a preconception, that there are no SMD electrolytics that may sound well.
Until someone gives me some reasonable and objective explanation for that, I think there are SMD electrolytics that may sound good.
Someone made any comparisons?
I've used the electric skillet method on hundreds of PCBs with great success. I put a dab of solder on each pad using a fine pitch iron and then a dab of flux on each little solder ball. Place the components on and heat, the surface tension "snaps" them into place with professional results.
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