Combining SMT and through hole

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ruffrecords

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I use a lot of 1/4W resistors in my designs, often mounted vertically with the pads 0.2 inches apart. I was wondering if I changed the pad shape to rectangular I could fit either a leaded or an SMT resistor. Is there a standard sized SMT resistor that would fit? Would the through hole bother the soldering of an SMT part instead?

Cheers

Ian
 

ccaudle

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Would the through hole bother the soldering of an SMT part instead?
Yes, solder will tend to wick down the via. What you can do is make the pair of SMD pads right beside the through-hole pads, joined with copper pour, with just enough space between to add a solder mask "dam" between the SMD pads and the through-hole vias. It doesn't take much obstruction to keep the solder from flowing, the surface tension tends to hold it in place if it is not being pulled along somewhere by capillary action, so as long as you are using solder mask and not bare board it should be feasible.
 

JohnRoberts

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SMD resistors can be too small to use... (0201)... there are many that you could easily use.. Hand popping small smd is not so easy.

JR
 

MidnightArrakis

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I use a lot of 1/4W resistors in my designs, often mounted vertically with the pads 0.2 inches apart. I was wondering if I changed the pad shape to rectangular I could fit either a leaded or an SMT resistor. Is there a standard sized SMT resistor that would fit? Would the through hole bother the soldering of an SMT part instead?

Cheers

Ian
[mounted vertically with the pads 0.2 inches apart] -- Edge-to-Edge? Or, Center-to-Center?

[Is there a standard sized SMT resistor that would fit?] -- Depends upon the answer up above.

[Would the through hole bother the soldering of an SMT part instead?] -- As "ccaudle" has responded, "YES".....doing so can cause some soldering problems, but they can also be dealt with (depending on how the PCB is being assembled).

What you are speaking of is what could be technically called "Via-In-Pad" (i.e. the component Thru-Hole would be acting as a via). I have designed numerous PCB's for RF/microwave equipment using "Via-In-Pad" technology and the resolving of any potential issues were handled by either: A) using a via drill size small enough that any wicking either couldn't happen or it didn't matter, B) If the PCB was to be in sufficient quantity to be wave-soldered, then you can actually specify for "plugs" to be inserted into the via holes, or C) having the PCB's hand-soldered usually negated any problems anyway.

Another possible problem with "Via-In-Pad" technology, but this only really occurs during the wave-soldering process, is that due to thermal differentials during the wave-soldering some of the Surface-Mount components will "tombstone" or, will stand up vertically on the PCB instead of laying down flat. This then becomes a nightmare scene that requires extensive hand rework!!! NOT GOOD!!!

As JR has mentioned.....using 0201 Surface-Mount components on a PCB layout can be a challenge, even using a high-end CAD system. I once designed a "covert intelligence-gathering" PCB for The Department of Homeland Security that was only 1.25" (31.75mm) square, had 8-layers, was only 0.032" (0.8128mm) thick and used 4-mil (0.1016mm) track and spacing with 210 size 0201 passive components placed onto both sides of the PCB. That was one tough little booger to layout!!! However, in your case, perhaps a standard 1206 or an 0805 size resistor and/or capacitor might fit your need. I need an answer to the first question first. (NOTE: A 1206 size resistor is normally rated at 1/4-Watt).

/
 

swpaskett

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The only SMT resistors I use are 1206 packages. They're big enough I can hand solder them if I have to. I often will place 1206 pads between the pads spaced for a 1/4W resistor in parallel with the through hole part, that way i can use either. I do not mess with J-bends, a bias I picked up as a working stiff, I suppose. If I don't have the room to lay it flat I just plan on using a 1206 SMT part.
 

Newmarket

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I use a lot of 1/4W resistors in my designs, often mounted vertically with the pads 0.2 inches apart. I was wondering if I changed the pad shape to rectangular I could fit either a leaded or an SMT resistor. Is there a standard sized SMT resistor that would fit? Would the through hole bother the soldering of an SMT part instead?

Cheers

Ian

In general it should be fine if the geometry works.
How would these boards be assembled - by 'hand' or wave / reflow etc ?
 

ruffrecords

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Just to clarify, the 0,2 inch spacing is centre to centre and the boards will be hand soldered. The SMT resistors would need to be large enough to be assembled by someone in their 70s ;)

Cheers

Ian
 

JohnRoberts

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Just to clarify, the 0,2 inch spacing is centre to centre and the boards will be hand soldered. The SMT resistors would need to be large enough to be assembled by someone in their 70s ;)

Cheers

Ian
0.2" is relatively large for smd but for high quality audio performance*** larger is better. 2012 is a standard size (0.20x0.12). Hand soldering smd resistors can be done, even by old pharts, but it isn't easy, and depends on how tight the layout is (and if you are old for your age). You will also need an iron with a fine tip. I did a certain amount of SMD rework on my tuner PCB and I would tack SMD parts in place with my iron, then reflow with my hot air wand. Using propely sized and designed solder pads the SMD components will self center over the pads due to surface tension.

Maybe buy a few parts and start experimenting, I did lots of SMD work with just my iron before I invested in a hot air station. Hot air is the right tool for the job.

JR

*** resistors in very small SMD packages, suffer linearity issues, as I discovered while developing my outlet tester several years ago, resistors in small SMD packages could not properly tolerate the required 500V insulation testing standard.
 

Dan Kennedy

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What a bunch of whingers. Today's proto to build is 12 x 120mm, switching supply, 4-20 dac out, two by 4-20 ins, PIC, CAN, couple of low voltage linear regs, osc, several IC's are pads on bottom or leadless, all passives are 0603 or 0402. Whaaa.
 

Andy Peters

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What a bunch of whingers. Today's proto to build is 12 x 120mm, switching supply, 4-20 dac out, two by 4-20 ins, PIC, CAN, couple of low voltage linear regs, osc, several IC's are pads on bottom or leadless, all passives are 0603 or 0402. Whaaa.
I'm with Dan here.

All SMT, all lead-free, since, oh, I don't even remember any more. Anyone can solder 0603 passives or 0.5mm-pitch QFP with the proper tools and some patience. Hell, have a stencil made, spooge the solder paste onto the board through the stencil, place the parts with tweezers and hit it with a hot-air rework tool.

The only non-SMT parts I use are connectors. OK, I lied. I'm using a serial SRAM in DIP-8 for something because the SMT version is unobtanium and Mouser had a thousand of the DIPs in stock. But no sockets!
 

Newmarket

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I'm with Dan here.

All SMT, all lead-free, since, oh, I don't even remember any more. Anyone can solder 0603 passives or 0.5mm-pitch QFP with the proper tools and some patience. Hell, have a stencil made, spooge the solder paste onto the board through the stencil, place the parts with tweezers and hit it with a hot-air rework tool.

The only non-SMT parts I use are connectors. OK, I lied. I'm using a serial SRAM in DIP-8 for something because the SMT version is unobtanium and Mouser had a thousand of the DIPs in stock. But no sockets!

Agree in general. Good magnification is key. Doesn't have to be expensive. In commercial applications I've used a 'Mantis' that runs into four figures (£) but also an inexpensive lamp / magnifier. Mantis was better but inexpensive option got the job done for low volume stuff working for an outfit with no capital to speak of !
Wrt the narrow pitch SMT. For low volumes a stencil might not be economic unless there is a source of 'standard' stencils at lower cost than custom ?
I've done narrow pitch stuff myself by hand. Whatever the pitch is of the SMT THAT Outsmarts device. But I might be wary of selling the result as a full on commercial product depending on my mood at the time 😳
 

ruffrecords

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What a bunch of whingers. Today's proto to build is 12 x 120mm, switching supply, 4-20 dac out, two by 4-20 ins, PIC, CAN, couple of low voltage linear regs, osc, several IC's are pads on bottom or leadless, all passives are 0603 or 0402. Whaaa.
There is no benefit per se in using SMT for DIY builds. As soon as they make SMT tubes, 10uF 400V film caps, 1:10 mic transformers and Carnhill output transformers in SMT - that's when I'll go the whole hog. Right now I just have a 26 x 252mm front panel PCB with 5 rotary switches, 10 toggles, 10 connectors, a pot and little room in between for them for the necessary passives.

Cheers

Ian
 

Dan Kennedy

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How about the front end cards for my Purifi modules for my power amp build? 50 x 60mm, LM5018 and LM317L for gate drive supply, LT3045 and LT3094 for low voltage regs, THAT1200 input chip, ADA-4898-2 for gain and low-Z drive, plus 13 aluminum electrolytics, 7 pins of 2.54mm header, 5 fastons, 34 pin right angle connector, various passives to make it all work?

That's my DIY. Only tube I might use anytime soon would be a 5840 in a mic, maybe. And I am fairly fossilized, been four eyes since 1960, fading memory, go to bed by 9:30.
 

JohnRoberts

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There is no benefit per se in using SMT for DIY builds. As soon as they make SMT tubes, 10uF 400V film caps, 1:10 mic transformers and Carnhill output transformers in SMT - that's when I'll go the whole hog. Right now I just have a 26 x 252mm front panel PCB with 5 rotary switches, 10 toggles, 10 connectors, a pot and little room in between for them for the necessary passives.

Cheers

Ian
except for new ICs that are only available in SMD packages. If you are content to only use old technology ignore SMD, but at some point trough hole components will become scarce and/or more expensive. Good luck

JR
 

Ricardus

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except for new ICs that are only available in SMD packages. If you are content to only use old technology ignore SMD, but at some point trough hole components will become scarce and/or more expensive. Good luck

JR
And SMD packages will get so small humans won't be able to reliably work with them.

WE NEED TO MAKE OUR STAND HERE.

Seriously. Robots are replacing us everywhere. When SMD parts get too small for humans to work with, where are we as hobbyists?
 

john12ax7

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With 0.200" spacing and 0.040" holes that would leave 0.160" between them. A 1206 would fit and be easy to hand solder. As mentioned solder will want to go into the hole, but that shouldn't be a performance issue at audio frequencies.
 

NOON

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I do a bit of both depending on the project, always low volume hand soldered. For what you're describing on a front panel board I always use smd these days. 1206 is easy enough to hand solder under a magnifying lamp and once you get the hang of it it's faster because you save time on lead bending and clipping and the constant board flipping. Give it a go, just be prepared to feel like a clumsy idiot for the first couple of hundred components or so because you're developing new muscle memory for the new techniques.
 

Newmarket

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With 0.200" spacing and 0.040" holes that would leave 0.160" between them. A 1206 would fit and be easy to hand solder. As mentioned solder will want to go into the hole, but that shouldn't be a performance issue at audio frequencies.
0.16" = 4.064mm
1206 is (approx - - specs vary very slightly) 3.2 mm length
Leaving 0.432mm to 'bridge' on each side (assuming 1206 is placed centrally).
But the gap may be less than 4.064mm depending on the OD of the resistor pads.
 

Newmarket

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I do a bit of both depending on the project, always low volume hand soldered. For what you're describing on a front panel board I always use smd these days. 1206 is easy enough to hand solder under a magnifying lamp and once you get the hang of it it's faster because you save time on lead bending and clipping and the constant board flipping. Give it a go, just be prepared to feel like a clumsy idiot for the first couple of hundred components or so because you're developing new muscle memory for the new techniques.

Also - have cocktail sticks to hand to move / press SMT around - for those times where the thing just wants to 'stick' to your metal tweezers etc.
And don't do what I thought was good idea once and get cheap nylon tweezers - they didn't appreciate the heat :rolleyes:
 

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