Nowadays, the PCB (Printed Circuit Board) design become so compact that most of the electronic components on the boards are surface mount devices (SMD). Since the size of the SMDs are usually small and most of time the pitch between two pins is tiny too, it is kind of tricky to do good SMD soldering. Here, we prepare a list of tips and find the resources for you to help you master the SMD soldering so that you can do not just good but amazing soldering work with SMD.
How to solder SMDs
Chips with lots of pins? Two approaches to this.
It requires that the device is heavy enough so that it is not movable by the hot air from the hot air gun. You can follow these three simple steps to get the job done.
a. Apply the solder to the pads with the solder paste. (notice that the solder paste already contain flux; no need to re-flux)
b. Align the chip pins to the corresponding pads
c. Use hot air gun to blow the hot air at low speed until the solder melts. (if you do not have a hot air gun, please check this post.)
2. Solder one corner pin first approach
If the device that needs to be soldered is too light, then you have to apply this approach. It is 4 step process.
a. apply flux on the corresponding pads.
b. align the chip and solder one pin down to the board.
c. solder another pin on the opposite corner.
d. drag solder the rest of the pins.
We strongly recommend to use a flux pen for surface mount device soldering since you can apply the flux exactly where you want it to be!
How about those tiny SMDs with 2 or 3 pins such as 603 capacitors/resistors
These devices are so small that you can not apply the solder paste plus the hot air gun approach. But, you can follow this 3 step process to get it done.
a. apply the solder flux
b. position the device correctly and solder one pin
c. solder the other pin
All these sound so easy? Well, in reality you may run into solder bridge issue. Basically, it means that the solder on one pin touches the solder on its neighbor pins. How to solve it? The solder wick is your best friend. What you need to do is to remove the excessive solder with solder wick to get rid of the solder bridge issue.
How to desolder SMDs
The goal of desoldering is to melt the solder on all the pins at the same time so that you can remove the devices. How to do that? There are two ways to it.
1. Desolder with the hot air gun (rework station)
With the hot air gun, you can melt the solder on all the pins at the same time. Along the way, you can use the solder wick to remove the solder.
2. Or, you can use ChipQuik
It is a magic product. So far, our favorite choice to desolder SMD with lots of pins. In case you do not know this product, please check it out here. It makes the SMD desoldering so easy and effortless. When you apply it to the pins that you need to desolder. You literally just lower the melting temperature of the solder already on the pins. With that, you can simply use a soldering iron (drag across all the pins) to melt them at the same time. No hot air gun is needed!
If you are more of a visual person, here is a YouTube video from SparkysWidgets that covers some of what we talked about here. It is a great soldering video. Great thanks to SparkysWidgets!
At 10:30, it talks about how to desolder the SMD chips with the hot air gun. At 18:25, how to solder the chips (with lots of pin) with drag solder. At 23:30, how to deal with the solder bridge.
A few things to remeber
a. do not forget to put flux before the soldering
b. after soldering, clean the board with the isopropanol alcohol. Believe or not, the flux may eat the board trace!
Expert tips for SMD soldering
If you master all the stuff we just talked about, you are at the SMD soldering advanced level. But, here is one video we found and love so much. We strongly recommend you to check it out. There are so many good tips that you do not want to miss this video. If you can apply all the tips from this video from Mike, I am pretty sure that you are at the expert level for SMD soldering. Nothing can stop you. If you think you are good at SMD soldering, this tutorial will open your eyes. Kudos to Mike for your brilliant tips for SMD soldering!
Hope all the tips we have here you help you become great at the surface mount device soldering. If you have any question, please contact us via the contact form.