Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

SMD vs. Through Hole Caps

Status
Not open for further replies.

Mark_R

Member
Happy new year!

On a surface mount projects the larger caps are usually still through hole mount. Obviously there is a size limit to what is available in SMD, but I was trying to understand the logic of not using SMD.

For instance, my project calls for a 25V 470uf alum. elec. cap. In looking at numerous surface mount PCBs made by others, I see that generally the caps in this size range or bigger are through hole, yet looking at the supplier inventory one can get an SMD cap of this size (it's still an aluminum can but mounted on a SMD adapter base Digi-Key - PCE3909CT-ND (Manufacturer - EEE-1EA471P) ) for similar price and availability, so why don't I see them in widespread use? Wouldn't minimizing the amount of through hole components be a priority or is that not a big deal in mass production?

Is there a rule of thumb at wht size on generally switches from SMD to TH?

Thanks.
 
Probably physical durability, through hole leads are much more durable than the solder only joint of SMD. Some multilayer boards because of routing issues might not be able to have at through hole at a specific location so a surface mount cap would be used. Least that's what makes sense to me.
 
You may prefer t.h. electrolytic capacitors for their longer life, expressed in hours at rated ripple current and temperature. You often have to choose bigger electrolytic capacitors to meet ripple current requirements, for example in power supplies, etc.; in this case there is a size limit for SMD parts, as you said.
On the other side, SMD capacitors are attractive because assembling boards without t.h. parts would be much cheaper.
 
Last edited:
SMT electrolytics are useful because they can be reflow soldered. Through hole components require wave soldering. If you have a board that is entirely SMT, then using a leaded capacitor means you just added an entire step in the manufacturing process. Also, drill hits cost money. SMT caps might only need 1 via or maybe not any to hit the power/signals they are connecting to.
 
SMT electrolytics are useful because they can be reflow soldered. Through hole components require wave soldering. If you have a board that is entirely SMT, then using a leaded capacitor means you just added an entire step in the manufacturing process. Also, drill hits cost money. SMT caps might only need 1 via or maybe not any to hit the power/signals they are connecting to.

My point exactly. Other than mechanical strength as mentioned by Sceadwian, the SMD seem to make sense, yet looking at a dozen or so SMD boards from various sources, I can't find but one example of the SMD caps being used. They're all radial TH. Digikey has a bazillion of them however, so someone must be using them.
 
What about your motherboard? THose are all SMD electrolytic caps.
 
Last edited:
On the design that my company makes, we still use a through-board capacitor, for several reasons:-

Price of components
Availability
Cost of feeder for pick and place machine
Larger components are more difficult to reflow

Also we have a low headroom so the surface mount device is taller than a radial capacitor.
 
On the design that my company makes, we still use a through-board capacitor, for several reasons:-

Price of components
Availability
Cost of feeder for pick and place machine
Larger components are more difficult to reflow

Also we have a low headroom so the surface mount device is taller than a radial capacitor.

So my question to you is this. Does your company use only thru hole or is it a mix of thru hole and smt? I am thinking the former since if you used mixed technology then the feeder cost would not seem like such an issue.

My opinion on SMT v.s. Thru hole is this; Much like the technologies of the fifties when thru hole technology replaced point to point wiring, smt is to thru hole. The advantages of smt far outweigh that of thru hole technology.

With today's high density board design, trace routing becomes more problematic and thru hole parts rob layout designers of valuable board real estate, add additional routing problems that violate design requirements, force mechanical size problems, design trade-offs and an increase in cost.

Another consideration is the PCB cost of adding plated thru hole in a board as each hole cost money. Furthermore part manufacturers are now producing less thru hole parts as smt is becoming the norm. I think if one looks past the present and more down the road, smt will become the mainstay and those companies that wish to not invest in new feeder machines will find themselves in trouble.

Well that is just my opinion.
 
Last edited:
From my experience, SMD electrolytic capacitors with voltage rating > 35V are not common and their cost might be greater than manual insertion + wave soldering of t.h. caps. If you are talking mainly about digital designs, using (low-voltage) SMD electrolytic capacitors is probably the rule.
For analog designs where higher voltage ratings and ripple currents are required, choosing t.h. capacitors is still your best option.
 
Last edited:
Agreed, there are parts that require thru hole insertion or even point wiring such as monster size caps, but overall the designer must consider part selection and minimize mixing thru hole and smt technologies. Project engineers of a cutting edge company will snap your head back if you fail to understand the manufacturing processes required to use mixed mounting technologies.

I think the designer must consider what manufacturing tools available in the company and act accordingly. In the long run, factories need to meet the changes of the industry or they are sure to encounter bumps.
 
So my question to you is this. Does your company use only thru hole or is it a mix of thru hole and smt? I am thinking the former since if you used mixed technology then the feeder cost would not seem like such an issue.

The vast majority of the components we use are SMT. The board in question has somewhere around 120 components on it.

We can pay something like £230 for a feeder that takes 8mm tape, and we can load reels that take 10,000 off 0603 size components. Many such components are used multiple times on each board so we really get our money's worth out of the feeder. On other designs, other values will fit in the same feeder.

A feeder for the big capacitor would cost nearly £1000 and would only be used once per board, and the reels can only take 500 pieces so would need loading more often. The feeder probably couldn't be used on our other designs. Add to that the fact that the capacitor goes on the other side from the surface mount components, and the headroom is too low for a surface mount electrolytic, and it becomes much easier to just mount a through board component by hand.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top