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SMT Resistor Sizes
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Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now.
Dave |
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For the smaller components I hold them down with a toothpick and tack a couple leads , then solder them
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On Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote: |
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Check Mouser Electronics. They usually have what you need and you can get it much faster than eBay and you will know exactly what you are getting! Sam Reaves
ARS W3OHM
Owner and Moderator of: LeCroy Owners Group on 开云体育 (Current and Future Group)
Electronics and Mechanical Hardware Design Engineering Manager Andritz Rolls Global Research Center (RETIRED) On Thu, Oct 29, 2020 at 12:31 PM Dave <theschemer@...> wrote: Ok, just a followup on my looking for physically large sized SMT |
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I find that 1206 resistors are good to start with, as well as 1206 parts.? They're not the cheapest (805 and 603 are frequently cheaper).
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I use SO outline parts and not TSSOP.? I use metcal soldering equipment and have a binocular microscope (check the distance between the stage and optics, since some are designed for chip inspection and give you no working distance).? Weller 1500 series would work well, but I prefer metcal. I generally find that 805 works for me, with some 603 as needed. I'm working with 0.5 mm TQFP-100 and TQFP-144 pin chips (FPGAs and video display chips), and find that the bypass capacitors take up too much space otherwise. Some chips require such small capacitors. I avoid BGA like the plague, and QFN packages can be difficult to solder to. Harvey On 10/29/2020 12:30 PM, Dave wrote:
Ok, just a followup on my looking for physically large sized SMT resistors. I researched yet again and realize that the physical size is based on the max watt rating, which I already knew (but probably forgot). And for my first attempts of making SMT boards I want large sized components for ease or working with them. So using a 0.120 inch length resistor (3/4 watt) where I only need a 1/4 watt resistor is the only way to do it. So now that I looked at ebay yet again I see I can get what I need at least in most of the sizes I desire for now. |
开云体育Good point Sam. I just need to make a large enough list so I can
save on shipping and not be buying 100 here and 100 there. On 10/29/2020 11:57 AM, Sam Reaves
wrote:
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I tin one pad for small parts, touch the pad with the soldering iron tip an use it for a stop.? Then with tweezers, slide the chip onto the pad.? Then solder the other end, being aware that the heat on the other pad could transfer over to the first pad and melt the solder there.? Be quick.
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One student I had was employed part time.? He tried to solder SMT resistors using a set of soldering tweezers to do both sides at once.? It caused much amusement amongst the other technicians.? I fixed that by explaining a better method, certainly soldering one side at a time. On larger TQFP chips, make sure that you solder one pin on one side then solder the opposite side.? Soldering one side completely can pull the chip out of alignment. I found a set of anti-static tweezers from Amazon worked well for holding parts. Harvey On 10/29/2020 1:01 PM, keith wrote:
For the smaller components I hold them down with a toothpick and tack a couple leads , then solder themOn Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote: |
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Harvey,
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? But you are advanced and I am noob. :-) But I can deal with the 1206 size and they are about 1/8" long at 0.120". Lots of projects in the future and still have to put together my reflow oven. I get my size info from here: I have not advanced to video chips or anything like it and likely won't. But I am still having fun. I have read about a lot of those packages you mention and have even watched videos on soldering them and some people make it look easy. And I would have never thought the way they do it is how it is done. Makes it look way easier than I first imagine. I have a nice microscope still in the box though for when I advance. Well what I mean is when I move a truckload of stuff that is in the way to set it up properly once and for all. :) Most all my soldering is done on the kitchen counter for now... Dave On 10/29/2020 12:11 PM, Harvey White wrote:
I find that 1206 resistors are good to start with, as well as 1206 parts.? They're not the cheapest (805 and 603 are frequently cheaper). |
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I have seen some cheater component home made tools here on the forum before. I guess everyone has their own way and all of them likely work.
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Thanks On 10/29/2020 12:01 PM, keith wrote:
For the smaller components I hold them down with a toothpick and tack a couple leads , then solder themOn Oct 29, 2020, at 12:32 PM, Dave <theschemer@...> wrote: |
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On 29/10/2020 17:20, Harvey White wrote:
I find using kapton tape to stick the big square chips (eg TQFP, LQFP etc) down the best - it's too easy to move the chip out of alignment while trying to solder the first pin (especially the smaller square chips). So I cut a piece of kapton tape, stick it to the top of the chip, and then holding the tape align the chip under a magnifying glass, then once aligned just push the tape down onto the board. At that point I can drag solder one row of pins then remove the tape. |
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Harvey,
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? I have seen that method used a lot ion YouTube videos. Looks easy enough. I have a nice set of tweezers in my kit. On 10/29/2020 12:20 PM, Harvey White wrote:
I tin one pad for small parts, touch the pad with the soldering iron tip an use it for a stop.? Then with tweezers, slide the chip onto the pad.? Then solder the other end, being aware that the heat on the other pad could transfer over to the first pad and melt the solder there.? Be quick. |
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I use mostly 0805 parts, though I do occasionally use 0603. I use 1206 when I want to run a trace between the pads, easier than using a jumper. I use a lighted magnifier rather than a scope. Get the best one you can afford since it can also be used for inspection and lots of other things. When stuffing the boards I usually tin one pad of several parts, solder the parts on that pad, then go back and solder the other side of them all. This cuts down on the problem Harvey notes below wherein soldering the second side results in unsoldering the first side. Once you get started with smt, you will never go back to through-hole. It's cheaper, easier, faster, and no holes need be drilled if you are making your own pcbs. Mark At 01:20 PM 10/29/2020, you wrote: I tin one pad for small parts, touch the pad with the soldering iron tip an use it for a stop.?? Then with tweezers, slide the chip onto the pad.?? Then solder the other end, being aware that the heat on the other pad could transfer over to the first pad and melt the solder there.?? Be quick. |
开云体育Mark, All good info. I have all the parts ( )
to build a reflow oven but also have too many irons in the fire as
usual. Once that is ready and I use stencils for applying paste,
the smaller parts will be much easier to deal with. I just bought
a bunch of 1206 series resistors. I was thinking the same thing as
I have read it elsewhere many times that once you start with SMD,
you won't go back to the the through-hole method. I can make my
own boards but now that I have ordered some I think the ones I
make will be the prototypes and I will order them after I test
them. Of course I am just a hobbyist so nothing to exciting... On 10/29/2020 4:32 PM, Mark Lerman
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I sometimes use soldering tweezers to solder parts. The trick is to use your tweezers to hold down the part (one tine of curved tweezers works well) after tinning & fluxing both pads. Gets harder as the parts get smaller, as usual.
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Tony -----Original Message----- |
Sam Reaves
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