A novice electronics repairman has a huge number of questions. Engaged in soldering work, both SMD components and BGA chips, for more than 8 years, the masters of Bgacenter have prepared for you a comprehensive guide on soldering. You can also learn soldering for beginners under the guidance of specialists, here is a professional soldering program.
The process of soldering bga chips, for convenience, is divided into several consecutive steps. The main ones are:
Before performing soldering work, carefully inspect the place of the upcoming soldering. Namely: which chips are located next to each other, whether there are those that are covered with a compound (we place heat sinks on them), which chips are located on the back side of the motherboard.
If you solder the chips, and on the other side is the CPU or BB_RF; try to pull the chip a little and not let the solder completely melt under the chip. This is the so-called cold soldering, which allows you not to heat the chips located on the reverse side. In this case, we risk tearing off the nickels on the contact pad, but they can then be restored. In addition, more often open pacifiers-unused contacts.
It is important to consider the ambient temperature. That is, in winter, if the room is cool or there are drafts, the temperature should be raised a little higher by 20-30 degrees Celsius.
After conducting a visual inspection, it is necessary to determine the direction of the hot air flow. The general rule is the direction of the hair dryer from the chips on the compound. Then we install the heat sinks of the chip with the compound. Use tweezers to “try on” the chip. How it will be captured, from which side the blade will start (we remove the chips on the compound with a spatula). If necessary, remove part of the binding, then restore the binding before soldering U.
Set the temperature on the hair dryer to 320-340 degrees Celsius. The air flow rate is an individual value for each thermal air soldering station.
Direct the hair dryer to the board, for 5-7 seconds, (preheat the board) raise the temperature of the soldering site. To avoid thermal deformations of the motherboard. And for uniform heating. The flux spreads and is evenly distributed over the desired area.
Air flow. This is individual. A lot depends on how close you are soldering from the element. I solder close to the element, almost close. And on a large stream. Due to this, the time of exposure to hot air on the board is reduced. The flow must be selected, there are 2 criteria here:
Apply the flux around the perimeter of the chip, since the board is hot, it immediately spreads and flows under the chip. The flux is necessary for a uniform temperature distribution. Start the hair dryer as vertically as possible. And we begin to warm up the chip, constantly making circular movements, for uniform heating.
The moment of removing the chip. You can navigate by time (earlier, 7 years ago (: drunk I counted the seconds in my head) or by a nearby capacitor. If the capacitor moves freely, I warm it for another 5 seconds, then a slight horizontal shift to the side, and then raise it. If you immediately lift it vertically up, it is possible to break off the nickels. I try not to allow the duration of heating more than 20 seconds. Some BGA chips have a glass case and it is important not to damage it. If there is at least a small chip or scratch on the chip body during soldering, I change the chip using a donor board.
With a thin-tipped soldering iron, apply the Rose alloy to each pin on the contact pad. This is necessary to lower the temperature of the factory lead-free solder. If you are afraid to tear off the contacts (or when you have little experience) when working with a soldering iron, you can tin the braid with Rose alloy and already tin the contacts on the contact pad with the braid. At the same time, special attention is paid to the binding, very easily and imperceptibly you can “remove” the radio components and then you will need to restore them before installing the chip.
Apply flux to the braid and without pressing on the board (put the soldering iron and pulled the braid) collect the remaining solder from the contact pad.
Use a cotton swab or a toothbrush soaked in BR-2 technical gasoline (or alcohol) to clean the contact pad from the flux residues. Before washing, lower the temperature of the board. As I understand it, when it is already possible to wash with gasoline? The finger is placed on the board, and if the finger tolerates, then you can also use gasoline, to avoid damage to the board.
Set the temperature on the hair dryer to 240-250 degrees Celsius. With a special spatula or tweezers, remove the remnants of the compound from the contact pad, from under the chip, and be sure to clean the perimeter. Often, very small radio components are installed around the chips and filled with a compound. Therefore, special attention is paid when cleaning the compound so as not to tear off the binding together with the glue. To do this, it is recommended to warm up the board for a sufficient time to soften the glue. And remove the compound in layers, and not immediately to the full depth. Finally wash the soldering place.
When performing repairs, in the mode of diode ringing, measure the voltage drop at each contact. Be sure to let the board cool down and only then perform measurements. Hot capacitors can show short circuit, and when their temperature drops, short circuit will not show.
Place the chip on a special mat, on top of which place a napkin or a piece of denim.
To restore the ball pins on the chip, you need to remove the existing solder. With a soldering iron, you can tin all the pins on the chip with a Rose alloy (for large NAND Flash or Wi-Fi chips, small chips can not be tinned with a Rose, but immediately collect the solder with a copper braid). Be careful with the glass cases, the pins are easily damaged and then do not get stale.
Apply the flux to the chip and use a braid with a soldering iron to collect the solder mixed with Roze. If necessary, remove the remaining compound from the surface of the chip. Wash the chip with a cotton swab or a toothbrush.
Choose a stencil. First, under a microscope, evaluate the condition of the stencil (the quality of the cut, contamination with paste or flux), if necessary, wash the stencil with gasoline or replace it. Combine the stencil with the chip and press it with tweezers. Use a spatula to apply a little paste to the stencil and rub the bga paste into the holes. Remove excess paste with a spatula and a cotton swab.
From this point on, and during subsequent knurling, do not allow horizontal and vertical displacements of the knurled chip relative to the stencil.
Lower the temperature on the hair dryer to about 250-270 degrees Celsius. The air flow can also be reduced compared to the flow during disassembly. Direct the hair dryer to the stencil and warm it up around the perimeter, performing circular movements. Evaporate the flux from the paste and finally form the conclusions on the chip.
With a dental probe or tweezers, push the chip out of the stencil (pushing it into the corner contacts). This must be done before the chip has cooled down, otherwise it will get stuck in the stencil.
Additionally, once again warm up the newly formed contacts with a hair dryer, for the final formation of the balls.
If the harness was shifted when lifting the chip, first restore the harness, only then work with the chip. On the hair dryer, set T = 280-320 degrees Celsius (depending on the paste used) and reduce the air flow, compared to the flow during evaporation.
Apply a small amount of flux to the contact pad. if there is a lot of flux, the chip will float in it.
Set the chip on the gaps and on the key:
Direct the hot air flow to the soldered chip. If the chip blows off the board, start the hair dryer on top. In this case, the air will press down on the chip and it will not move. And it can also blow away the chip, because the master forgot to add the flux — . In no case should you put pressure on the chip from above.
How to understand that the chip is soldered:
Wash the flux from the motherboard.
Lower the board temperature before checking. You can not connect to the LBP and supply power to the hot board immediately after soldering. Since there are lines, most often these are the main power lines of the processor and RAM, which have low resistance. And when the voltage is applied to the hot board, the LBP can register a short circuit. Connect the board to the laboratory and apply the voltage, starting from 0 volts, gradually bring it to the working 3.8 Volts. If the soldering is done efficiently, then the current consumption on the unit will not show.
Software used by Bgacenter masters: Wuxinji, JCID, Xinjijao. Each software has its own advantages and disadvantages. The main software is Wuxinji.
A necessary and sufficient set of equipment and consumables to perform independent repairs of the motherboards of phones, tablets and laptops.
Thermal Air Soldering Station
Laboratory power supply unit
Silicone heat-resistant mat
1.5 and 2.0 mm solder removal braid
Soldering for a novice master is a fascinating process. Independent development of which will require not only significant material, but also financial investments. It is clear that experience comes with practice. And the more of this practice, the more professional the soldering master becomes. But there is one thing — – it is better to start under the guidance of experienced masters. Who, having a large background, are ready to share their knowledge and experience with others.