Oven for drying chips
Examples of completed stencils
Fig.1 Examples of completed stencils for restoring BGA balls
Fig.2 Refurbished ball leads of the BGA chip
Necessary equipment
Introduction
Security Methods
Ventilation:
Flux fumes during soldering and desoldering can be harmful. Use general or local exhaust to comply with Maximum Permissible Concentration standards harmful substances at work. Consult the Technical Data Sheet (MSDS) for soldering materials O permissible norm MPC.
Personal protective equipment:
The chemicals used in the reballing process may cause damage to areas of the skin. Use appropriate safety equipment when performing cleaning, soldering or desoldering activities
Lead Hazards:
The USEPA Carcinogen Assessment Group classifies lead and its alloys as teratogens, and its components as Class B-2 carcinogens.
When working with static-sensitive components, ensure that your work area is static-free by using the following:
Component susceptibility
Sensitivity to humidity
Plastic BGA packages are moisture absorbent. The chip manufacturer designates the component's sensitivity level on each package. Each sensitivity level has a time limit for external influence associated with it. The JEDEC standard reflects the time limit for external exposure at standard atmospheric pressure, 30 degrees C and 60% relative humidity. Our instructions also provide a table of humidity levels (see information below).
Susceptibility to static charge
The sequence of removing, reballing, and reinstalling a component onto a PCB creates multiple chances for static damage to damage the component. Try to use appropriate protective equipment
If the permitted exposure time is exceeded, the JEDEC standard requires drying of the component. The standard drying time is 24 hours at 125 degrees C. After drying, the component should be placed in a bag with a moisture-absorbing substance, which will prevent moisture from re-entering it. This drying will prepare the component for the soldering process.
Sensitivity to temperature
BGA components are susceptible to temperature changes in the following cases:
Shock Susceptibility
Internal shocks occur due to thermal gradients and stresses within the chip structure. Thermal shocks are more noticeable during the reballing process, even when both types of shocks are present. To minimize the risk of temperature shock, carefully monitor the process temperature cycle. Heating uniformity is critical to minimizing shock to the chip.
The process of removing ball leads (deballing)
There are many tools that allow you to remove solder residue from a BGA component. These include hot air vacuum tools, tip soldering irons and, most preferably, low temperature wave soldering units (220 degrees C.) Any of these tools, if correct use allows for reballing.
Since soldering irons with good temperature control for soldering are not so rare these days and are relatively inexpensive, we will describe the deballing process using a soldering iron with a tip. Stay confident throughout the deballing process because... it contains many mechanical and thermal stresses that are potentially harmful to the chip.
Tools and materials
Preparation
Note: It is recommended to dry the component to remove moisture before deballing it.
 | Step 1 - Apply Flux to the Chip Place the chip on a conductive mat, pad side up. Too little flux will make the deballing process difficult. |
Fig.3 Scratched pads of the BGA chip | Step 2 - Removing the Balls Using a desoldering wire and a soldering iron, remove the solder balls from the chip's pads. Place the braid on top of the flux, then heat it with a soldering iron from above. Before moving the braid along the surface of the chip, wait until the soldering iron warms it up and melts the solder balls. ATTENTION: Do not press on the chip with a soldering iron. Excessive pressure may damage the chip or scratch the contact pads (see Fig. 3). For achievement best results, clean the chip using a clean piece of braid. A small amount of solder should remain on the pads to make reballing easier. |
 | Step 3 - Cleaning the Chip Clean the chip immediately using a cloth soaked in isopropyl alcohol. Timely cleaning of the chip will make it easier to remove flux residues. Remove the napkin from the bag and unfold it. By wiping the surface of the chip, remove the flux from it. Gradually move the chip while wiping to cleaner areas of the napkin. Always support the opposite side of the chip when cleaning. Do not bend the corners of the chip. Note:
|
 Fig.4 Clean BGA surface
Fig.5 Dirty BGA surface | Step 4 - Check It is recommended that the inspection be carried out under a microscope. Check for clean pads, damaged pads, and missing solder balls. (See Fig. 4 and 5) Note: Since the flux is corrosive, additional cleaning is recommended if the chip is not reballed immediately. |
 | Step 5 - Additional Cleaning Apply deionized water to the contact pads of the chip and scrub them with a brush (you can use a regular toothbrush). Note: For best results, brush the chip in one direction first, then rotate it 90 degrees and brush in the other direction as well. Then clean it in a circular motion. |
 | Step 6 - Flush Clean the chip thoroughly with a brush and rinse with deionized water. This will help remove any remaining flux from the chip. Then dry the chip with dry air. Recheck the surface (Step 4). If the chip will lie for some time without the applied balls, you need to make sure. That its surface is very clean. Immersing the chip in water for any length of time is NOT RECOMMENDED. |
The process of applying ball leads (reballing)
Tools and materials
Preparation
 | Step 1 - Inserting the Stencil Place the stencil in the clamp. Make sure the stencil is hung tightly. If the stencil is bent or dented in the clamp, the restoration process will not work. This is usually a consequence of contamination of the clamp or poor adjustment of it to the stencil. |
 | Step 2 - Apply flux to the chip Use a syringe to apply a small amount of flux to the chip. Note: Before you start, make sure. that the chip surface is clean. |
 | Step 3 - Distributing flux over the surface of the chip Using a brush, spread the flux evenly along the side of the contact pads of the BGA chip. Try to coat each pad with a thin layer of flux. Make sure all pads are coated with flux. A thinner layer of flux works better than a thicker layer. |
 | Step 4 - Inserting the Chip Place the BGA component in the fixture, with the flux-coated side facing the stencil. |
 | Step 5 - Upsetting the Component Place the stencil and component in the clamp by gently pressing on the component. Make sure the component sits flat against the stencil. |
 | Step 6 - Reflow Place the fixative in a hot convection oven or hot air reballing station and start and run the reflow cycle. In any case, the equipment used must be configured to the thermal profile developed for the BGA chip. |
 | Step 7 - Cooling Using tweezers, remove the retainer from the oven or reballing station and place it in the conductive tray. Leave the chip to cool for about a couple of minutes before removing it from the retainer. |
 | Step 8 - Removing the BGA Chip Once the chip has cooled, remove it from the retainer and place it in the cleaning tray, ball side up. |
 | Step 9 - Soaking Apply deionized water to the BGA stencil and wait about thirty seconds before continuing. |
 | Step 10 - Removing the Stencil Using fine tweezers, remove the stencil from the chip. It is best to start from a corner, gradually removing the stencil. The stencil must be removed in one go. If it suddenly doesn't come off, add more deionized water and wait another 15 to 30 seconds before continuing. |
 | Step 11 - Cleaning Up Dirt Fragments It is possible that small pieces of particles or dirt will remain after removing the stencil. Remove them with tweezers. Just gently move one tip of the tweezers between the balls of the component, grabbing the particles with the other. ATTENTION: The tip of the tweezers is sharp and can scratch the solder mask on the chip if you are not careful. |
 | Step 12 - Cleaning Immediately after removing the stencil from the chip, clean the egeo with deionized water. Apply a small amount of deionized water and scrub the chip with a brush. ATTENTION: Support the chip while brushing to avoid mechanical stress. Note: For best cleaning results, first scrub the brush in one direction, then turn it 90 degrees and scrub in the other. Complete the cleaning process with circular movements of the brush. |
 | Step 13 - Flushing the BGA Chip Rinse the chip with deionized water. This will help remove small particles of flux and dirt left behind from previous cleaning steps. Let the chip air dry. Do not wipe it with napkins or cloths. |
 Fig.6 Clean BGA balls
Figure 7. Corrosion residues at the base of the balls | Step 14 - Checking the quality of application Use a microscope to check the chip for contamination, missing beads, or flux residue. If you need to clean again, repeat steps 11 - 13. ATTENTION: Since the process does not use clean-free flux, careful cleaning is necessary to prevent corrosion and further failure of the chip. Note: Steps 9 - 13 are carried out unambiguously. At some other stages it is also possible to use spray cleaning. |
Cleaning the Retainer
As the BGA reballing process progresses, the fixative becomes increasingly sticky and dirty. Rice. 8 shows traces of contamination on the fastener. It is necessary to clean the remaining flux from the clamp so that the stencil fits correctly. The process described below applies to both flexible and rigid fasteners. For better cleaning, it’s a good idea to use an ultrasonic cleaning bath
Tools and materials
 | Step 1 - Soaking Soak the BGA stencil fixative in warm deionized water for approximately 15 minutes. |
 | Step 2 - Cleaning with Deionized Water Remove the retainer from the water and scrub it with a brush. |
 | Step 3 - Flushing the Retainer Rinse the retainer with deionized water. Let it air dry. |
Chip drying
The drying procedure is very important to ensure that there is no popcorn effect during the chip reballing process. It is highly recommended to dry the chip before each reballing operation to prevent the presence of moisture for a further period of time.
Preparation
Step 1 - Chip Humidity Level
Select the desired chip humidity level from the table below to determine the time required to dry the BGA component. The BGA manufacturer is required to indicate the level of sensitivity of the chip to humidity. It is also necessary to know the exposure time environment to your chips. If the exposure time exceeds the chip's sensitivity level by 2-5 times, 24 hours of drying at 125 degrees C is required.
Note:
If you are not sure about the time the chips are exposed to the external atmosphere, it is better to assume that it has been exceeded.
SMT component moisture/reflow temperature specifications can be found in the IPC/JEDEC J-STD 033A standard.
ATTENTION:
Never dry BGA components in plastic trays made from a material with a melting point less than 135 degrees C. Moreover, do not use trays that are not clearly marked with their maximum operating temperature.
Do not allow the solder balls to touch metal surfaces during the drying process.
Step 2 - Drying
Set the oven temperature and time according to the humidity level. When the oven reaches required temperature, place BGA components into it.
Step 3 - Dry Packing
Once drying is complete, place the components in a static-protected moisture-proof bag with a fresh dose of desiccant. A desiccant will help you keep components dry during storage and transportation.
Moisture Susceptibility Level Chart
| Susceptibility level | Exposure time (outside the protective bag) at 30 degrees C/60% relative humidity or as expected |
| 1 | Unlimited when<= 30 градусов C/85% относительной влажности |
| 2 | 1 year |
| 2a | 4 weeks |
| 3 | 168 hours |
| 4 | 72 hours |
| 5 | 48 hours |
| 5a | 24 hours |
| 6 | Forced drying before installation. After drying, it must be installed within the time indicated on it. |
Latch setting
The best clamp used in most cases is the fixed clamp because it does not require pre-adjustment. Of course, there may not be fixed latches for all types of BGAs. This is the field of activity for flexible, customizable fasteners. The movable clamp can be adjusted to any type and size of BGA component from 5mm - 57mm, as well as for rectangular components.
Fig. 10 Clamp with lost perpendicularity | Step 1 - Adjusting the Movable Latch Loosen all end screws so that the parts of the clamp can move freely, but the angles between them are maintained. Note: Do not loosen the screws too much. If the screws are loosened too much, it will be difficult to keep the clamp square (see Figure 10). |
 Fig. 11 Location of the step for mounting the chip | Step 2 - Determine the required dimensions of the retainer Adjust the clamp so that the chip fits tightly into it, then tighten the screws. In Fig. 11, arrows show the location of the step on the latch. The chip in the latch “sits” on these steps, and the setting of the latch should make it easy to remove the chip from it if necessary. |
 Fig. 12 Bending of the stencil when fixing it | Step 3 — Checking the BGA Stencil Fit The last step is to check the installation of the chip in the clamp along with the stencil, to check the fit of the clamp and adjust it if necessary. ATTENTION: The stencil should not bend or bend after it is fixed. (example Fig. 12). If the stencil does not fit into the clamp without bending, readjust the clamp. Note: Figure 11 shows the stencil on top of the chip, just to better show the curve of the stencil. In fact, during the installation process, the chip should be on top of the stencil. |
Reflow Temperature Profile
As with all soldering processes, the temperature profile is a key element to a successful process. The process of reballing a BGA chip itself is quite simple and repeatable; setting up the temperature profile for hot air reflow equipment takes much more time.
Each BGA chip may require a different temperature profile. Start with the basic profile shown below, making adjustments for BGA material type, BGA chip weight and size should yield acceptable results.
Please note that the profile setting is based on the measured component temperature. The temperature in the oven itself is usually different from it.
ATTENTION: Do not heat the component above 220 degrees C, as... this may cause it to fail.
Any hot air equipment equipped with:
Key points:
Measuring component temperature
To create a working temperature profile, thermocouples are placed in different areas of the component, and their readings are monitored using special software, which allows you to find the optimal reflow profile of the component. This reading method ensures uniform heating readings and minimal thermal shock to the component being tested.
The air flow around the component causes it to heat up. When a component is heated unevenly, temperature gradients (temperature changes) occur in its composition. A large temperature gradient results in thermal shock, which can damage the component.
FAQ
Q - How do I know if a component is clean enough?
A - The best way to tell if a component is clean enough is to use an ionograph or other similar equipment to detect ionic contaminants.
Q - What should the lead balls look like after the reballing process?
A - After reflow, the balls on the BGA component should be spherical and smooth. Their surface structure, like the skin of an orange, indicates that the reflow time is too long, the reflow temperature is too hot, or the cooling process is too slow.
Q - The stencil sticks to the component while it is being removed. What can I do?
A - Apply more water and let the stencil soak for a longer time. This usually helps. Increasing the water temperature can also have a positive effect. When this problem occurs, it usually means that the reflow cycle is too hot or too long.
B - One of the balls did not stick to the contact pad. What can I do?
A - The use of flux and temperature profiling is often the cause of these ball contact problems. Apply a small amount of flux to the pad and place a separate ball of flux on it, then melt it. This will allow you to secure the ball that was not soldered the first time. If there are too many of these balls, deball the chip and repeat the process of applying ball pins.
B — After several cycles of use, the stencils no longer adhere clearly to the clamp. What can be wrong?
A - Flux can build up on the inside of the fastener and cause problems with fixing the stencil. Clean the retainer according to the instructions above.
Modern radio-electronic devices cannot be imagined without microcircuits - complex parts into which, in fact, dozens, or even hundreds of simple, elementary components are integrated.
Microchips make devices light and compact. You have to pay for this with the convenience and ease of installation and the rather high price of the parts. The price of a microcircuit does not play an important role in determining the overall price of the product in which it is used. If such a part is damaged during installation, when replacing it with a new one, the cost may increase significantly. It is not difficult to solder a thick wire, a large resistor or a capacitor, all you need is basic soldering skills. The microcircuit must be soldered in a completely different way.
To avoid annoying misunderstandings, when soldering microcircuits it is necessary to use certain tools and follow certain rules based on extensive experience and knowledge.
To solder microcircuits, you can use various soldering equipment, ranging from the simplest soldering iron to complex devices and soldering stations using infrared radiation.
A soldering iron for soldering microcircuits should be low-power, preferably designed for a supply voltage of 12 V. The tip of such a soldering iron should be sharply sharpened to a cone and well tinned.
To desolder microcircuits, a vacuum desoldering pump can be used - a tool that allows you to remove solder from the legs on the board one by one. This tool is similar to a syringe in which the piston is spring-loaded upward. Before starting work, it is pressed into the body and fixed, and when necessary, it is released by pressing a button and rises under the action of a spring, collecting solder from the contact.
A hot-air station is considered a more advanced equipment, which allows both dismantling of microcircuits and soldering with hot air. This station has in its arsenal a hairdryer with adjustable air flow temperature.
A piece of equipment such as a heat table is very popular when soldering microcircuits. It heats the board from below, while installation or dismantling is carried out from above. Optionally, the heating table can be equipped with top heating.
On an industrial scale, soldering of microcircuits is carried out by special machines using infrared radiation. In this case, the circuit is preheated, soldered directly, and the contacts of the legs are cooled step by step.
Soldering microcircuits at home may be required to repair complex household appliances and computer motherboards.
As a rule, to solder the legs of the microcircuit, use a soldering iron or soldering gun.
Working with a soldering iron is carried out using regular solder or solder paste.
Recently, lead-free solder with a higher melting point has become increasingly used for soldering. This is necessary to reduce the harmful effects of lead on the body.
To solder microcircuits, in addition to the soldering equipment itself, you will need some other equipment.
If the microcircuit is new and made in a BGA package, then the solder is already applied to the legs in the form of small balls. Hence the name - Ball Grid Array, which means an array of balls. These enclosures are designed for surface mounting. This means that the part is installed on the board, and each leg is soldered to the contact pads with a quick, precise action.
If the microcircuit has already been used in another device and is used as used spare parts, it is necessary to perform a reballing. Reballing is the process of restoring the solder balls on the legs. Sometimes it is also used in the case of a blade - loss of contact of the legs with the contact patches.
To carry out reballing, you will need a stencil - a plate of refractory material with holes located in accordance with the location of the microcircuit pins. There are ready-made universal stencils for several of the most common types of microcircuits.
For proper soldering of microcircuits, certain conditions must be met. If the work is carried out with a soldering iron, then its tip should be well tinned.
For this, flux is used - a substance that dissolves the oxide film and protects the tip from oxidation before being coated with solder during soldering of the microcircuit.
The most common flux is pine rosin in a solid, crystalline form. But to solder a microcircuit, such a flux is not suitable. Its legs and contact spots are treated with liquid flux. You can make it yourself by dissolving rosin in alcohol or acid, or you can buy it ready-made.
In this case, it is more convenient to use solder in the form of filler wire. Sometimes it may contain powdered rosin flux inside. You can purchase a ready-made soldering kit for soldering microcircuits, which includes rosin, liquid flux with a brush, and several types of solder.
When reballing, solder paste is used, which is a base of viscous material that contains tiny balls of solder and flux. This paste is applied in a thin layer to the legs of the microcircuit from the back of the stencil. After this, the paste is heated with a hairdryer or infrared soldering iron until the solder and rosin melt. After hardening, they form balls on the legs of the microcircuit.
Before starting work, it is necessary to prepare all tools, materials and devices so that they are at hand.
When installing or dismantling, the board can be placed on a thermal table. If a soldering gun is used for dismantling, then to prevent its impact on other components, you need to isolate them. This can be done by installing plates made of refractory material, for example, strips cut from old circuit boards that have become unusable.
When using a desoldering pump for dismantling, the process is more accurate, but takes longer. The desoldering pump “charges” as it cleans each leg. As it fills with pieces of solidified solder, it needs to be cleaned.
There are several soldering rules that must be followed:
Electronic parts are very sensitive to static electricity. Therefore, when assembling, it is better to use an antistatic mat that is placed under the board.
Chips are microcircuits housed in BGA packages. The name, apparently, came from an abbreviation that meant “Numerical Integrated Processor”.
Based on experience, professionals have a strong opinion that during storage, transportation, and shipment, chips absorb moisture and during soldering, it increases in volume and destroys the part.
The effect of moisture on the chip can be seen if the latter is heated. Blisters and bubbles will form on its surface long before the temperature rises to a value sufficient to melt the solder. One can only imagine what is happening inside the part.
To avoid the undesirable consequences of moisture in the chip body, when installing boards, the chips are dried before soldering. This procedure helps remove moisture from the case.
Drying of chips must be carried out observing temperature conditions and duration. New chips that were purchased in a store, from a warehouse, or sent by mail are recommended to be dried for at least 24 hours at a temperature of 125 °C. For this you can use special drying ovens. You can dry the chip by placing it on a hot plate.
The drying temperature must be controlled to prevent overheating and failure of the part.
If the chips were dried and stored under normal room conditions before installation, it is enough to dry them for 8-10 hours.
Considering the cost of the parts, it is obviously better to dry them in order to proceed with installation with confidence, than to try to solder an undried chip. Troubles can result not only in wasted money, but also in lost time.
It is known that if a chip is damp, then when you try to solder such a chip, it will swell with bubbles and will not work properly. And taking into account the cost of chips, their delivery time and the complexity of repairs, this is very expensive. I searched a lot on the Internet. There are different tips, from drying it on a table lamp to using a household oven. There is also very expensive equipment. None of the advice suited me personally (like my friend in Germany, he had been looking for something similar for a long time.). In theory, each chip should have documentation that describes at what temperature and how long it should dry before soldering. This is correct, but not always available to most repairmen.
If we summarize all the information, it turns out that for normal drying of the chip, it must be at a temperature of approximately 130 degrees Celsius. about 8-10 hours. This does not harm it, but it does remove moisture. I do not claim originality, but I want to share the device that I use myself and my friend in Germany (I did it on my advice). Perhaps it will be useful to others too. Since using this device, there have never been any problems with any chip; I ordered it from both China and Russia.
Oven for chips made from scrap materials over a couple of weekends. The body is made of pressed paper with lamination. These were pieces from decorative furniture trim, 6 mm thick. Although you can use any temperature-resistant material (must keep the temperature at least up to 180 degrees C. and higher). Connections are made with M3 screws. 20-watt ceramic resistors with a nominal value of 15 Ohms were used as heating elements (you can use from 10 to 18 Ohms). Only 6 pieces, since the oven is designed for simultaneous drying of 2-3 chips.
For one chip, 3-4 resistors will be enough. An electro-mechanical thermostat at 130 degrees C was used as a temperature maintaining element. For protection (not pictured), a 10 A, 180 degree C thermal fuse is pressed to one of the resistors from below. All resistors are connected in parallel. Those. the entire circuit consists of series-connected: a thermal fuse, a thermostat, a group of resistors. For clarity, a 12 V LED (or 3.5 V through a 510 Ohm resistor) is connected in parallel with the resistors. The entire device is powered by a computer power supply (there was an old one with 200 W). Although any 12 V power source and a current of about 5 A will be suitable. A cover made of the same material as the body is placed on top of the device. This improves thermal stability and reduces switching frequency.
Pros: ease of manufacture and availability of materials. (Thermostat and resistors can be purchased at almost any radio store).
Of the minuses: The thermostat has a very large hysteresis, almost 40 degrees C. That is, it turns off at 130 degrees C, and turns on at 90 degrees C. But this does not harm the chip in any way; rather, on the contrary, it does not allow a very damp chip to swell. The photo shows the device from below (without wires and thermal fuse) and actually in operation. The device has been in use for about a year. I hope this information will be useful!
