Soldering bga chips
How to solder circuit boards? And how does BGA stand for? These two frequently asked questions are answered by the bgacenter masters during soldering courses. From English-ball grid array, that is, an array of balls that looks like a grid. Solder balls are applied to the chip through a stencil, then a stream of hot air melts the solder itself and the correct shape of the contacts is formed.
And the soldering process consists of a certain sequence of actions, observing which we get a high-quality connection. But there are a large number of nuances, for which they come to study. Starting from what angle and at what distance from the Board to keep the nozzle of the hair dryer, temperature modes of dismantling and mounting chips, which side to start the blade. And many other subtleties that the current master of the service center may know. And the one who can confirm their level of completed repairs.
Soldering the chip
90 % of the repair success rate depends on the correct disassembly of the chips. It is at this stage that it is important not to tear off the nickels and damage the chip with high temperature. And begin soldering the chip, with the removal of the compound.
Compound – a polymer resin, usually black or brown, used in the manufacture of phone system boards. Purpose of the compound:
- Additional fixation of radio components and bga chips on the Board.
- Protection of non-isolated contacts from moisture.
- Increase the strength of the Board.
The most important chips, such as: CPU, BB_RF, EEPROM, NAND Flash, Wi-Fi in the factory after installation, are filled with compound. And before you perform dismantling, you need to clear the perimeter of the resin.
The sequence of dismantling
1. Carefully inspect the Board for previous repairs.
2. Perform diagnostics and make the necessary measurements.
3. Prepare the Board for soldering, remove protective screens, stickers. Disconnect and remove the coaxial cable. Attach the motherboard to the appropriate holder.
4. Remove the compound around the chip being disassembled. The temperature on the hair dryer is 210-240 degrees Celsius.
5. Install heat sinks. The place of installation of heat sinks depends on the location of the soldered chip.
6. Use a hair dryer to warm up the Board for a few seconds. Thus, we increase the temperature of the Board, so that the
flux spreads evenly.
7. Apply FluxPlus, or any other non-flushing flux, to the surface of the chip.
8. Direct the hot air flow to the soldered element. The temperature during disassembly is 340 degrees Celsius. How do I know that the solder has melted and it’s time to remove the chip from the Board? There are several ways to do this:
- Track the time using a stopwatch.
- Count down the seconds to yourself.
- “Push” with a probe or tweezers the chip itself or a nearby binding (capacitors, resistors or coils). As soon as the chip starts to shift, by a fraction of a millimeter, it is time to wind the blade under or use tweezers.
9. Prepare the contact platform. For this:
- use a special spatula to remove the remaining compound;
- zaludit alloy rose without exception, all the contacts;
- use the braid to collect the remaining solder from the work surface;
- after cooling the motherboard to room temperature, wash the contact pad with alcohol, BR-2 or DEGREASER.
10. The Board is prepared for the installation of a serviceable chip.
Soldering bga chips
The General principle of soldering is as follows: due to the surface tension created when the solder melts, the chip is fixed relative to the contact pad on the system Board. The soldering temperature of bga chips on iPhone boards is 320-350 degrees Celsius.
Preparation of the chip:
- Use a special knife to clean the compound.
- Remove the remaining solder with a 1 or 2 mm copper braid (depending on the chip’s geometric size).
- To recover the ball conclusions. There are two ways to generate conclusions:
- BGA paste is applied to the surface of the chip via a stencil (priority method) Used in most cases.
- Manually, with BGA balls. This option is suitable for ships with a small number of pins, up to 50. Although a few years ago, when the quality of stencils left much to be desired) modems on the iPhone 5S were rolled manually. That is, each ball, with a probe or tweezers, was installed separately. And this is 383 contacts, zxw calculated.
- If you work with paste, be sure to warm up the chip with a hair dryer after removing the stencil to form the correct shape of the contacts. Additionally, fine-grained sandpaper, P500 GOST R 52381-2005 can be used for these purposes.
- Finally clean the chip with alcohol and a toothbrush.
- Solder the chip to the contact pad, setting it according to the key and gaps.
Bottom heating for BGA soldering
To reduce the time when the Board is exposed to high temperatures, the Board is heated. We recommend the STM 10-6 monoblock PCB heater. Stable maintenance of the set temperature over the entire area of the heating element contributes to uniform heating of the entire motherboard (depends on the heater model). And another advantage over other thermostats is a convenient universal mounting system.
BGA soldering flux
On the market represented a huge number of manufacturers of fluxes. Bga center uses the widely used FluxPlus. Pay attention to the date of manufacture and expiration date of the flux. The advantages of flux-gel:
- non-washable (many masters recommend washing it anyway);
- convenient dispenser, hence the high accuracy of dosing during soldering operations;
- does not emit unpleasant odors;
- provides good spreading of the solder on the base metal, thereby reducing the surface tension of the molten solder.
Thermal air soldering station
Purpose of the Quick 861DE ESD Lead station-soldering (dismantling and installation) BGA chips and SMD components. Advantages of this station:
- three memory modes CH1, CH2, CH3;
- high performance “over the air”, Quick 861DE is suitable for soldering boards and phones and laptops;
- temperature stability.
What can be improved in the design of the station is the temperature control not by buttons, but by rotating controllers, as on the Quick 857D (W)+.
Soldering iron for soldering
PS-900 METCAL-induction soldering system. The power of the soldering iron 60 W is enough to work with multilayer boards of modern electronics. The experience of phone repair engineers with this soldering iron is 4 years. What are the distinctive features of the PS-900:
- no calibration required,
- large selection of tips,
- reliability of the station, the consumable material is the inductor. With daily intensive soldering, replacement of the inductor on average 1 time in 10 months.
For the novice master on repair of phones, a good option would be a microscope СМ0745. Binocular microscope with a focal length of 145 mm (when installing a Barlow scattering lens). Purpose of the lens system, increasing the focal length while maintaining the working area.
The advantage СМ0745:
- Smooth magnification is achieved by using a cremallera.
- The lens system is made of glass, not plastic.
- The ability to complete the head of the microscope with different tables and tripods.
- Magnification to 45X.
For soldering iPhone boards, mainly used solder balls with a diameter of 0.2 mm. Usually delivered in a glass container, 10,000 balls in each jar.
Composition of solder balls:
- tin 63%,
- lead 37%.
The quality of the soldering
After performing the soldering work, make sure that the BGA soldering is performed efficiently. Control is performed in several ways:
- Turning on the device
For more information about verification methods, read the following article.