Homemade flux for soldering bga chips. How to re-solder a BGA chip. What we should know about flux

The flux ensures stable combustion, promotes the formation of a reliable welded joint, removes unnecessary impurities from the welding zone and generally improves the quality of work. can be bought in the store, modern manufacturers offer a large assortment. But we suggest you make the flux yourself. It won't take much time, but it will save you money.

Mainly, soldering flux is used for welding and small parts. There is also a special flux for bga soldering. In this article we will share the “recipe” for making various types flux or, more simply put, solder, which can be used in most small soldering jobs.

Before you start making flux, you need to understand its types and features. To connect two parts you need to hold them in the welding zone a certain temperature, depending on the metal it can vary greatly. In this case, the melting temperature of the solder should be noticeably higher than the melting temperature of the metal you are working with. This leads to the specifics of choice. You need to consider the materials you are joining together, their melting point and strength.

Generally speaking, fluxes are hard and soft. Hard fluxes have a high melting point, while soft fluxes have a low melting point. They are also called refractory and low-melting. If the part to be welded is thin, use a soft flux. If it is larger in diameter and requires long-term heating, then use hard refractory solder.

Refractory flux (or solder) melts at a very high temperature (from 400 degrees Celsius) and ensures the formation of a strong one. But when using such a flux, parts often overheat and may not work. This problem is especially relevant for radio engineers and anyone who is interested in electronics.

Low-melting flux melts at low temperatures and allows you to use it when working with boards and circuits, for example. This flux consists mostly of lead and to a lesser extent of tin. It may additionally contain impurities of other metals. There are separate low-melting fluxes that melt at temperatures up to 150 degrees. They are used when working with transistors.

A high-quality flux should conduct heat unhindered, ensure the strength of the welded joint, have good stretchability, protect against corrosion and be resistant to the melting temperature of the metal.

Regardless of the type of flux you use, the soldering area after work should be wiped with a rag pre-moistened in acetone. The seam itself can be cleaned using a small stiff brush previously soaked in solvent.

Soldering itself as a method of joining metals has a number of advantages. With its help you can achieve a durable and airtight seal that is resistant to corrosion and oxidation. Also, soldering does not require special skills; this work can be performed by a person with minimal theoretical knowledge.

Instructions for making flux

So, how to make soldering flux with your own hands? It all depends on the destination. If you need to solder thin ones, then you can use rods with a diameter of 1 mm. We will make them ourselves.

We will need a small bottle or any other vessel with a flat bottom. We make a hole in the bottom with the diameter we need (in this case 1-2 mm). We take lead or tin and melt it using gas burner. Pour it into our bottle. Molten metal will begin to flow out of the hole; you need to prepare the surface in advance. You can use a sheet of tin, for example. The resulting “rods” must harden, then they need to be cut. Experienced craftsmen use special molds to make rods. Also look at the review of bga soldering flux.

We will need rosin crystals, which need to be crushed into powder. Wrap the crystals in a thick cloth and tap them with a hammer (preferably a wood hammer or a meat mallet). Mix the powder and alcohol in a one to one ratio. Alcohol can be purchased at a pharmacy. It is advisable to mix in a glass container, such as a small jar. Thoroughly mix the alcohol with the powder and place the jar in hot water. Mix everything thoroughly again until it has a homogeneous consistency. Ready! The resulting flux can be used with a medical syringe or poured into an empty nail polish bottle.

For good soldering of BGA chips you need high-quality gumboil– the quality or possibility of soldering in general depends on it.

When first getting acquainted with chip soldering or reballing, most people are in no hurry to buy real original fluxes popular manufacturers, and consider it sufficient to start by trying the Chinese equivalent. I will say unequivocally: soldering with cheap Chinese flux and original ones are two completely different things. I was convinced of this during the first attempt to roll balls through a stencil onto a chip from a video card. I used the most popular Chinese flux RMA-223. Its price in the aliexpress store is the most attractive. Nothing worked for me: several balls constantly did not want to lie on the contact pads, so I had to repeat the procedure several times. Moreover, if at the first attempt of melting the balls they did not stick to the platform, then after any amount of heating it is useless.

This led me to search quick solution. To begin with, I tried to repeat the procedure with alcohol rosin. It didn’t work out, because the rosin burned, and the balls simply didn’t have time to melt. But I noticed that those that melted instantly fell on the platforms.

The main feature of fluxes for BGA soldering is the ability long time retain their properties when high temperatures and no boiling. As for Chinese flux, it does not darken or burn out at high temperatures, but its flux properties leave much to be desired.

Therefore, the idea came to modify the Chinese flux RMA-223 by adding rosin to it (in my case, alcohol rosin), but for this it is necessary to get rid of alcohol, which will lead to the boiling of the flux at high temperatures. This recipe helped me a lot, I still use it to this day and not only for BGA soldering. Since it has a thick structure, the flux is convenient to apply when soldering SMD elements and other details. It is not necessary to wash it off after soldering.

So, you will need:

1. Chinese flux RMA-223

2. Alcohol rosin LTI-120 (can be replaced with other alcohol rosin)

3. Metal container for heating (I took an aluminum flask from under photographic film)

4. Mixing spatula (in my case, a pencil)

Procedure:

1. Squeeze RMA-223 flux into the container.

2. Heat the flux until it becomes liquid.

3. Add alcohol rosin LTI-120, in a ratio of approximately 1:3 (that is, LTI-120 - 25%, RMA-223 - 75%).

Heat the resulting liquid, stirring with a spatula until it boils gently. To warm up, I used a heat gun.

4. Continue heating until boiling stops or becomes very weak. This will indicate that the alcohol has evaporated from the liquid.

5. While the resulting flux is hot and liquid, draw it into syringes.

All! The flux is ready, after cooling, it will become as thick as initially and acquire the properties of a good flux. In comparison with the original fluxes, I personally didn’t notice any difference. It also provides high-quality soldering and is easily washed off without leaving stains or burns.

I hope you find this recipe useful.

In modern electronics, there is a steady trend towards increasingly dense installations. The consequence of this was the emergence of BGA packages. We will consider soldering these structures at home in the framework of this article.

general information

Initially, many pins were placed under the chip body. Thanks to this, they were placed in a small area. This allows you to save time and create ever smaller devices. But the presence of such an approach in manufacturing results in inconvenience during the repair of electronic equipment in BGA package. Soldering in this case should be as careful as possible and be carried out exactly according to technology.

What do you need for work?

You need to stock up:

1. where is the hot air gun?
2. With tweezers.
3. Solder paste.
4. Electrical tape.
5. Braid for removing solder.
6. Flux (preferably pine).
7. A stencil (to apply solder paste to the chip) or a spatula (but it’s better to stick with the first option).

Soldering BGA packages is not difficult. But for it to be successfully implemented, it is necessary to prepare the work area. Also, to be able to repeat the actions described in the article, it is necessary to talk about the features. Then the technology for soldering microcircuits in a BGA package will not be difficult (if you understand the process).

Peculiarities

When explaining what the technology for soldering BGA packages is, it is necessary to note the conditions for the possibility of full repetition. So, stencils were used made in China. Their peculiarity is that here several chips are assembled on one large workpiece. Due to this, when heated, the stencil begins to bend. Big size panel leads to the fact that when heated, it takes away a significant amount of heat (that is, a radiator effect occurs). Because of this, it takes more time to warm up the chip (which negatively affects its performance). Also, such stencils are made using chemical etching. Therefore, the paste is not applied as easily as on laser-cut samples. It would be good if there were thermal seams. This will prevent the stencils from bending as they heat up. And finally, it should be noted that products made using laser cutting provide high accuracy (deviation does not exceed 5 microns). And thanks to this, you can simply and conveniently use the design for its intended purpose. This concludes the introduction, and we will study what the technology for soldering BGA cases at home involves.

Preparation

Before you begin to solder the microcircuit, you need to apply strokes along the edge of its body. This must be done if there is no silk-screen printing that indicates the position electronic component. This must be done to make it easier to later install the chip back on the board. The hairdryer should generate air with heat of 320-350 degrees Celsius. In this case, the air speed should be minimal (otherwise you will have to solder back the small items placed nearby). The hair dryer should be held so that it is perpendicular to the board. Warm it up in this way for about a minute. Moreover, the air should be directed not to the center, but along the perimeter (edges) of the board. This is necessary in order to avoid overheating of the crystal. Memory is especially sensitive to this. Then you should pry the chip by one edge and lift it above the board. However, you should not try to tear with all your might. After all, if the solder has not been completely melted, then there is a risk of tearing off the tracks. Sometimes, when applying flux and heating it, the solder will begin to form balls. In this case, their size will be uneven. And soldering microcircuits in a BGA package will be unsuccessful.

Cleaning

We apply alcohol rosin, heat it and get the collected garbage. Please note that such a mechanism should under no circumstances be used when working with soldering. This is due to the low specific coefficient. Then you should wash the work area, and it will be a good place. Then you should inspect the condition of the conclusions and assess whether it will be possible to install them in their old place. If the answer is negative, they should be replaced. Therefore, you should clean the boards and chips from old solder. There is also the possibility that the “nickel” on the board will be torn off (if using braid). In this case, a simple soldering iron can be of great help. Although some people use braid and hair dryer together. When performing manipulations, the integrity of the solder mask. If it is damaged, the solder will spread along the tracks. And then BGA soldering will fail.

Rolling new balls

You can use already prepared blanks. In this case, they simply need to be laid out on the contact pads and melted. But this is only suitable for a small number of pins (can you imagine a microcircuit with 250 “legs”?). Therefore, as a more easy way stencil technology is used. Thanks to her, work is done faster and with the same quality. The important thing here is to use a high-quality one. It will immediately turn into a shiny, smooth ball. A low-quality copy will disintegrate into a large number of small round “shards”. And in this case, it’s not even a fact that heating to 400 degrees and mixing with flux will help. For ease of operation, the microcircuit is fixed in a stencil. Solder paste is then applied using a spatula (although you can use your finger). Then, holding the stencil with tweezers, you need to melt the paste. The temperature of the hair dryer should not exceed 300 degrees Celsius. In this case, the device itself must be perpendicular to the paste. The stencil should be maintained until the solder has completely cured. After this, you can remove the fastening insulating tape and use a hairdryer, which will heat the air to 150 degrees Celsius, gently heat it until the flux begins to melt. After this, you can disconnect the microcircuit from the stencil. IN end result smooth balls will be obtained. The microcircuit is completely ready to be installed on the board. As you can see, soldering BGA packages is not difficult at home.

Fasteners

1. Turn the chip over so that the pins are facing up.
2. Apply the edge to the nickels so that they coincide with the balls.
3. We fix where the edges of the microcircuit should be (for this you can apply small scratches with a needle).
4. We fix one side first, then perpendicular to it. Thus, two scratches will be enough.
5. We place the microcircuit according to the designations and try to catch the nickels at the maximum height with the balls by touch.
6. Heat the work area until the solder is molten. If the previous steps were followed accurately, then the microcircuit should fall into place without any problems. The power that solder has will help her with this. In this case, it is necessary to apply just a little flux.

Conclusion

This is all called “technology of soldering microcircuits in a BGA package.” It should be noted that what is used here is not the soldering iron familiar to most radio amateurs, but a hair dryer. But despite this, BGA soldering shows good results. Therefore, they continue to use it and do so very successfully. Although the new has always frightened many, with practical experience this technology becomes a familiar tool.

BGA (B all G rid A rray) is a matrix of balls. That is, this is a type of microcircuit that has solder balls instead of terminals. There can be thousands of these balls on a chip!

Nowadays, BGA chips are used in microelectronics. They can often be seen on boards mobile phones, laptops, as well as in other miniature and complex devices.

In phone repairs, there are a lot of different breakdowns related specifically to microcircuits. These BGA chips may be responsible for certain functions in the phone. For example, one microcircuit may be responsible for power, another for Bluetooth, a third for the network, etc. Sometimes, when the phone falls, the balls of the BGA chip move away from the phone board and it turns out that the circuit is broken, therefore the phone loses some functions. In order to correct this issue, repairmen either heat the microcircuit so that the solder ball melts and again “grabs” with the contact pad on the phone board, or they completely dismantle the microcircuit and “roll” new balls using a stencil. The process of rolling balls onto a BGA chip is called reballing. In the Russian expanses this term has not taken root and in our country it is simply called “rolling”.

Our guinea pig will be a mobile phone board.

In order to make it easier to solder “those black squares” on the board, we will use, or popularly, “bottom heating”. We set the temperature on it to 200 degrees Celsius and go drink tea. After 5-7 minutes we begin to fend off our patient.

Let's focus on the BGA chip, which is simpler.

Now we need to prepare the tools and chemistry for soldering. We can't do without stencils for various BGA chips. Those who are seriously involved in repairing phones and computer equipment know how important thing. The photo below shows the entire set of stencils for a mobile phone repairman.

Stencils are used to “roll” new balls onto prepared BGA chips. There are universal stencils, that is, for any BGA chips. There are also specialized stencils for each microcircuit. At the very top of the photo we see specialized stencils. Bottom left - universal. If you choose the right pitch on the chip, you can easily roll balls onto any of them.

In order to reball a BGA chip, we also need these simple tools And Consumables:

Here is the familiar Flux-off to all of you. You can read more about it and other chemistry in the article Chemistry for an electronics engineer. Flus Plus, Solder Plus solder paste (gray mass in a syringe with a blue cap) is considered the best solder paste, unlike other pastes. The balls with it turn out like factory ones. The price for this paste is expensive, but it's worth it. Well, of course, among all the other junk there are also price tags (buy them so that they are very sticky) and a simple toothbrush. We will need all these tools to reball a simple BGA chip.

In order not to burn the elements located nearby, we will cover them with thermal tape.

Lubricate the microcircuit generously around the perimeter with FlusPlus flux

And we begin to warm up our BGA with a hairdryer over the entire area

This is where the most crucial moment comes when soldering such a microcircuit. Try to warm up air flow slightly less than average. Raise the temperature literally a couple of degrees. Doesn't unsolder? Add a little heat, and most importantly TAKE YOUR TIME! A minute, two, three... it doesn’t come off... add heat.

Some repairmen like to chatter “hahaha, I can unsolder the BGA in a matter of seconds!” They unsolder, then they unsolder, but at the same time they do not understand how much stress the soldered element and the printed circuit board receive, not to mention the nearby elements. I'll repeat it again, TAKE YOUR TIME, TRAIN ON CORDS. TAKE YOUR TIME tearing off an unsoldered microcircuit will backfire on you, because you will tear off all the dimes under the microcircuit! Use special devices for lifting microcircuits. I found them on Ali this link.

And so we heat our microcircuit with a hairdryer

and at the same time we check it using a chip extractor. I wrote about him in an article.

The microcircuit, ready for lifting, should “float” on the molten balls, let’s say... like a piece of meat on jellied meat. We lightly touch the microcircuit. If it moves and returns to its place, then carefully lift it with the help of antennae (in the photo above). If you don’t have such a device, then you can use tweezers. But be extremely careful! Don't use force!

Currently, there are also vacuum tweezers for microcircuits of this kind. There are manual vacuum tweezers, the operating principle of which is the same as that of the Desalt Pump

and there are also electric ones

I had hand tweezers. To be honest, she's still a piece of shit. Hardcore repairmen use an electric vacuum cleaner. One has only to bring such tweezers closer to the BGA chip, which is already “floating” on the molten balls of solder, and it immediately picks it up with its Velcro.

According to reviews, electric vacuum tweezers very convenient, but I still didn’t have a chance to use it. In short, if you decide to, go electric.

But let’s return to our microcircuit. With a tiny push, I make sure that the balls are really melted, and with a smooth upward movement I turn the BGA chip over. If there are many elements nearby, then it would be ideal to use vacuum electric tweezers or tweezers with curved jaws.

Hurray, we did it! Now we will practice soldering it back :-).

This is where the real thing begins difficult process– the process of rolling balls and soldering the microcircuit back. If you haven't forgotten, it's called rolling. To do this we must prepare a place for printed circuit board. Remove any solder that remains there. We lubricate the whole thing with flux:

and start removing all the solder from there using good old copper braiding. I would recommend the brand Goot wick. This copper braid has proven itself very well.

If the distance between the balls is very small, then use copper braiding. If the distance is large, then some repairmen do not resort to copper braiding, but take a fat drop of solder and, with the help of this drop, collect all the solder from the patches. The process of removing solder from BGA patches is a very delicate process. It is best to increase the temperature of the soldering iron tip by 10-15 degrees. It also happens that the copper braid does not have time to warm up and pulls out spots behind it. Be very careful.

and sand it using a simple toothbrush, or even better, a cotton swab dipped in Flux-Off.

It turned out something like this:

If you look closely, you can see that I still tore off some of the spots (there are black circles at the bottom of the microcircuit, instead of tin ones) But! Don't be upset, they are, as they say, single. That is, they are not electrically connected in any way to the phone board and are made simply to securely attach the microcircuit.

And now the most interesting and complex process begins - rolling balls onto the BGA chip. We put the prepared microcircuit on the price tag:

We find a stencil with the same pitch of the balls and attach the microcircuit to the bottom of the stencil using the price tag. Using your finger, rub Solder Plus solder paste into the holes of the stencil. It should look something like this:

We hold the tweezers with one hand and a hair dryer in the other and begin to fry at a temperature of approximately 320 degrees on a very low flow over the entire area where we rubbed the paste. I wasn’t able to hold the camera, hair dryer and tweezers in both hands at once, so there weren’t enough photos.

We remove the finished microcircuit from the stencil and lubricate it with a little flux. Next, heat with a hairdryer until the balls melt. We need this so that the balls fall evenly into place.

Let's see what we got as a result:

Damn, it's a little sloppy. Some balls are a little larger, others a little smaller. But all the same, this will not interfere at all when soldering this chip back onto the board.

We lightly lubricate the nickels with flux and put the microcircuit in its original place. Align the edges of the microcircuit on both sides according to the marks. There is only one mark in the photo below. Another mark is opposite it diagonally.

And using a very small air flow from a hairdryer with a temperature of 350-360 degrees, we seal our little thing. If sealed correctly, it should fit normally on its own, even if we are slightly skewed.

Where is the key for the BGA chip?

Let's look at the moment when we suddenly forgot how to install the microcircuit. I think all repairmen had this problem ;-). Let's take a closer look at our little thing through an electron microscope. In the red rectangle we see a circle. This is the so-called “key” from where all the BGA ball pins are counted.

Well, if you forgot how the microcircuit was installed on the phone board, then look for a circuit diagram for the phone (there are a dime a dozen of them on the Internet), in this case Nokia 3110C, and look at the arrangement of the elements.

Oops! Now we have found out which direction the key should be located!

For those who are too lazy to buy solder paste (it is very expensive), it will be easier to purchase ready-made balls and insert them into the holes of the BGA stencil.

I found a whole set of them on Ali, for example .

Conclusion

The future of electronics belongs to BGA chips. microBGA technology is also gaining great popularity, where the distance between the pins is even smaller! Not everyone will undertake to solder such microcircuits). In the repair industry, the future lies in modular repairs. Basically, now it all comes down to purchasing a separate module or an entire device. It’s not for nothing that smartphones are made monolithic, where both the display and the touchscreen already come together in one package. Some microcircuits, and indeed entire boards, are filled with a compound that makes it impossible to replace radio elements and microcircuits.