Basic knowledge of reflow

2022-05-07 34

This is the overview page of upper reflow surface mount components. It's a part of our surface mount welding. It may be easier than you think! Series.


Reflow soldering usually involves the application of solder paste, consisting of small beads of solder suspended in flux, with pads on the board, placing components on pads, and then heating the molten solder to create a joint assembly. There are various ways to apply the paste and heat the plate in various ways. Due to surface tension and other physical, reflow, during which parts will be "in place" even if they are relatively misaligned pads.


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Solder paste consists of small beads of solder suspended in flux. There are many types of solder paste, such as different types of solder. There are mixtures of lead-free and 60/40, 63/37 and others. There are different types of flows, and those that have residues, have to clean off the plates, and those that can be cleaned with water and those that don't need to be cleaned at all.


Some people swear Chester 256 solder paste. Sparkfun sells these two kinds of cheap lead and lead-free solder pastes.


As we have already said, many rules and SMT welding guidelines are for large-scale manufacturing. On this scale, even a few human notices of wooden boards can add delays and incur additional costs for manufacturers. When building boards by hand, many of these guidelines can be relaxed or even completely ignored. However, some can't.


Solder paste, like solder, has some nasty ingredients in it. It's a real lead-free and lead-free formula-so it's not enough lead. You don't want it on your skin, and you don't want to eat it. It's similar to solder wire, however, the solder paste particles are very small, and it can easily be on your fingers or under your nails. Many chemicals have no biological way to exit your body, so that they just build up gradually over time. It's not a bad idea, put on gloves, but be sure to wash your hands after. It is not very expensive soap to have even special leadership.


Be careful with your solder paste, folks. You don't want your children or pets to enter it. Do not store solder paste in the refrigerator where the food or drink will be stored.


When you are finished, clean your tools and work surfaces. Isopropyl alcohol is very effective. Don't turn you into a normal trash can-dispose of its waste in your local hazardous waste disposal facilities.


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Manufacturers and distributors usually store and ship solder paste in a refrigerated environment. They also indicate that the life of their solder paste is very short. And it depends on the exact wording of the paste. Many amateurs find that their solder paste works well because of the months of freezing. If you refrigerate it, please don't use the food or drink that used to be stored. There are all kinds of small, inexpensive semiconductor refrigerators "soda can be cooled", which can help prolong life without considering a lot of space. Those guys Adafruit converted into USB soda can cool the power of the machine from wall warts.


Solder wick

Or tin-sucking weaving, which can be used to repair solder bridging. It is made of thin copper wire woven flat, and sometimes there is flux in it. You usually use it with a soldering iron.


tweezers

Fine tweezers are essential for moving and holding surface mount components. We like the curved ones. You can get about $5, like these non-magnetic "micro-fine" curved tweezers are decent.


Some people use vacuum pick-up tools to pick up and place components. We don't want it.


Magnifying glass and light

You need plenty of light when soldering SMT, and you may want some amplification while working. There are 2.5 x magnifiers, such as OptiVisors, and built-in magnifying glasses with good head goggles.


When you finish your work, you may want a 10 X magnifying glass to check your work. Some even have 10 X magnifiers and built-in lighting!


mould

Solder paste is applied to a car by using a mold. Expensive molds are made of metal, while cheap ones are made of plastic. Polyimide is a very good plastic. Ohararp can take board document design and laser cutting Kapton mold for it.


Toaster oven

Some people use the oven for rearrangement. Once used for reflow soldering, the oven should be devoted to reflow soldering, not for food.


hot plate

We (and many others) really like hot plates for rearrangement. They are all cheap (


Sparkfun has a short video demonstration process. There are many others.



Manually apply paste.


For most of the larger bag types, you don't need a mold. It can speed up board making, but it can be pasted manually and applied. Solder paste can be dispensed manually, using syringes, and things like toothpicks. It is tolerant for amateurs to return. When applying paste manually, it is important to remember that although you need to paste on each pad, you may apply for too many pastes. Most of the molds are like 0.0035 inches thick-what you think is what you paste!


For the bag like SOIC, there are rows of needles there, just lift a thin line across the pad-there is no need to try each pad one by one.

Filling plate assembly

After the pads on the board are pasted with solder, the board must fill in the components. It is important to have enough light. If you need to, use magnification. Some components are polarized and need to be placed in a certain tendency. If you are not sure, check the kit description (or component data sheet).


We use tweezers to fill the board assembly, but some people use vacuum pick-up tools. These functions almost like gentle solder sucker rods, and apply suction to pick up components.


Components should be padded as accurately as possible, but the reflow process will line up the parts as long as they are close.

Check your work! Do you remember to fill all the components of the board? Are they all lined up correctly? Are they all facing the right direction?


reflow soldering


After the board is filled, it needs to be rearranged. This involves heating the solder paste. , flux acquisition is in progress, and mushy spread out. Solder melts, and the magic dance between pads, components and solder paste that you have been watching comes to a climax. Suddenly, the assembly lined up with the pad. Every time you see this, you really think anything is possible.

Although it depends on the specific solder paste, there are rearrangements of all components as soon as possible, and it is OK to turn off the heat. Ideally, no joints are liquid for more than sixty seconds.


But it's important to calm the board down and everyone will hit it. It's easy to get excited about your new project, pick it up, it's cool, and then once you realize it's too hot, touch it, and put it in the watch that you pick up and then all the components are shot off. If you are lucky, you will hear them bounce off the wall or hit the wall.


Check your work.


Check your work! Do all joints properly welded to the board of directors look? Use as much light as possible and as needed for amplification. Small bridges can be easily fixed with soldering irons. Heat the associated pins and "paint" the solder. Large bridges can be easily fixed with solder.


Remove the solder and solder.

If you want to use it, go beyond the union, put the braid in it, and put the braid on your iron plate. (Heat flux) into braid solder. End the braid, and if it doesn't seem to work, first, cut off a small piece of knitting from the bobbin and use it. Depending on the situation, the heat may follow the braid instead of heating the upper joint area. If the braid is old, the flux may not work. You can add flux to help pressurize the braid.


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