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Surface mount vs through hole, which is best?

The saying you “can’t teach old dogs new tricks” has some truth to it when you consider the extraordinary stubbornness of so many individuals. Such is the nature of some people who grew up when through hole technology was the only type to exist and then surface mount came along.

This is especially true for a lot of people I’ve encountered in the audio world, they still design with as many through hole components as possible! The beneficial aspects acquired with surface mount technology go well beyond making devices more compact and small but yet so many people are stuck in the ways of the old days.

While I am definitely first to acknowledge that not everything newer is better, this is a case where I feel that surface mount actually is superior in quality. Even with its exceeding benefits in some areas there will be instances where a mix of both is commonly a necessity. There is nothing more obvious than the Shorter lead lengths acquired through surface mount devices. This means a reduction in inductance and other parasitic elements. With a through hole part you may have 4-6mm of lead before you even get to inside the IC.

With a surface mount component you just have the small pin or pad with a bit of bonding trace internal to the IC. This certainly does make it much easier to get better performance in pcb layout where every fraction of a mm between a component and the IC can be of benefit in a design.[12:03 AM]Another benefit with a lot of surface mount passive components such as capacitors and resistors is how the ESL(another parasitic) is related to the amount of lead length and how there is typically less in surface mount packages. This is due to the end caps being direct as part of the component with no external lead.

Surface mount technology is also capable of providing higher precision in passive components which can be highly beneficial in signal circuits or filter circuits(high pass, low pass, crossover, etc) since it allows you to get a very precise and less variance RC(resistor capacitor)filter.

Yes through hole can get close but it can’t match the precision. Thermal performance can also be of benefit. For instance you can have a thermal pad on the bottom of the IC. This thermal pad can connect direct to the pcb’s surface ground, of which several layers can be tied together through vias , thereby creating a fairly large heat sink which may eliminate the need for having a heat sink external to the device in some situations. Still, even if it doesn’t, your are increasing the thermal dissipation of the device and therefore would only need a smaller heat sink. This also could benefit smaller and compact size.

Speaking of a compact size, surface mount also allows you to mount more various IC’s on both sides of the board. While you certainly still can mount some components on both sides with through hole parts, you are also breaking up the layers. For instance a typical 2 layer board may be power, signal, and ground all within 2 layers. With all surface mount parts you can route signals on a layer underneath some IC’s and components where as with through hole, you are drilling all the way through the board so there is less room for that.

So with surface mount you can definitely decreases board size by fitting more overall components. Can you imagine a laptop that is made with all through hole parts or a smart watch? They would be incredibly big and bulky devices.[12:03 AM]Why is it that some engineers hate the switch to surface mount? Well for one thing , those who grew up during through hole only parts have then needed to re-learn how to design with surface mount. Some of these parts are also super small! You aren’t going to solder some of these without looking at them under a microscope or in some cases with BGA (ball grid array) chips you may even need an X-ray check to assure the balls underneath are all pristinely soldered and separated from each other.

These components will also likely be soldered with hot air for the most part and sometimes soldering iron opposed to just a soldering iron for through hole parts. Therefore assembling surface mount devices may in some cases be more difficult or require more equipment. Conclusion: While through hole parts are sometimes necessary such as is the case with a lot of very high value electrolytic capacitors, polymer capacitors, film capacitors, and high power transistors, using surface mount when applicable to your design can be of benefit in many ways which is why ultimately I view it as a technological advancement and superior process.

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