BGA Rework how to operate [welding debugging]
Update date：2012-6-22
A, rework the basic concept
Surface assembly automation and assembly manufacturing process one should achieve high assembly pass rate and work, but 100% of the yield is still an unattainable the goal, no matter how perfect the process, there is always some assembly manufacturing can not control the factors that produce defective products. PCB assembly must be estimated defect rate and rework to make up for some of the problems in the product assembly process.
The traditional repair is usually done by skilled operators manual, but as more and more electronic products, precision assembly of miniature components, such as flip chip (FC), chip scale package (CSP), ball grid array (BGA) packaging, manual, can not meet the requirements, and need specialized repair equipment and to complete the repairing process.
This section of BGA components, for example, describes the general steps of the rework technology and process.
Second, the BGA component rework process
The basic steps of the BGA component rework; a temperature curve for each component, removal of components, removal of residual solder paste and cleaning of this area 'placement of BGA components. The heat-resistant temperature of most semiconductor components 240 to 260 ° C for the BGA component rework systems, heating temperature and uniformity control is very important. OK Group of hot air reflow soldering and rework system BGA-3592-G/GSP-3500-G and Japan M. s. En8ineerin8Co. Ltd. MS series rework station a good solution to this problem (U.S. OK Group launched the latest rework station BGA rework 5000).
The following is a brief description of the BGA component rework process.
A. Each AU parts, a temperature curve
The technical staff has a wealth of BGA component rework experience to rely on the destructive method to determine the appropriate temperature curve. Which drilling on the P, so that the solder joints exposed, and then connect the thermocouple to solder. In this way, we can each solder joint to be monitored to establish a temperature profile. Technical data indicate that the establishment of the PCB temperature curve is a covered components of the PCB-based, it uses a new thermocouple and a calibration record components, and installed in the PCB high and low temperature hot galvanic. Once the temperature curve for the A component of the substrate kimono can be programmed for reuse.
Rework system BGA components can be easily removed. Typically, a temperature (determined by the temperature curve), the hot air from the nozzle so that the solder paste reflow, but it will not damage the base pull or surrounding components. Different types of nozzles with the preferences of the equipment or technical personnel. The number of nozzles so that the top and bottom of the flow of hot air in the BGA components, move the hot air of the nozzle level, there are a number of nozzles only special hot air jet at the top of the BGA components. Some people like the nozzle for use with a hood, which can be directly hot air concentrated in components, thereby protecting the surrounding components. Removal of BGA components, it is very important to maintain the temperature. The key is to warm up to the bottom of the PCS, to prevent warping. The removal of Jesus A multi-reflow, and thus requires skill and patience. In addition, the return times a BGA components usually take 8-10 min, slower than other surface mount component rework.
Two. Pick in addition to components
Removal of chips if you do not intend to re-use, and P boat can withstand high temperatures, removal of the chip is available as a higher temperature (shorter heating cycle).
3. Li River wash
(1) cylinder wash weld the Ang cleaning pad will remove the chips remain in the PCB surface flux, solder paste out reason, the use of cleaning agents must meet the requirements. Order to ensure the Solder Joint Reliability of BGA components, are generally not long residual solder paste on the pad must be removed the old solder sterile, unless the re-formation of BGA solder balls on the chip.
Due to the small size of the BGA components, especially the smaller size of the C5P ELEMENTS cleaning pad is difficult to rework the CSP components, if the CSP components around a small space, they need to use no-clean flux.
Remove residual solder paste, many operators prefer to use desoldering braid. If you are using braid proper and correct use, remove the process will be fast, secure, efficient and cheap. Although used in addition to tin braided belt requires certain skills, but not difficult. Braid with a soldering iron and the selected contact with the need to remove the welding Crest, between the welding cell located in the tip and substrate, will not damage resistance of a good film or exposed printed line. The best way to pass to solder braid it so that the heat, so that the paddle shift or PCB Road by the possibility of damage occurs on down to members of low.
Welding core activity is very good in use, so you do not have to in order to avoid thermal damage to drag the solder core. On the contrary, the solder core is placed between the substrate and tip, heated 2-3s, and then up to pick up the braid and iron. Lift rather than drag the braid, enable the pad was the risk of damage to a minimum. Braid can remove all the residual welding glance, thus excluding the possibility of bridging and short-circuit. After the removal of residual solder paste with a suitable solvent to clean this area, you can use the brush to brush away the residual flux. The new components of the appropriate reflow soldering, the PCB must be very clean.
(2) Xu cover welding bud and flux coated solder paste on the PCB results have important implications for the the DGA components of repair. Through the selection of the chip matches the template, you can easily weld tone coated on the PCB. OK Group DGA-3500-G equipment, micro-optics on the system can easily verify that the solder paste to whether Xu evenly. Deal with the CSP components, you can choose three kinds of solder paste; an RMA solder paste no-clean solder sterile, water-soluble solder sterile. RMA solder paste reflow time can be slightly longer; use no-clean solder paste reflow temperature should be chosen low.
4. Patch
The main purpose of the patch is a ball on the BGA components on the PCB, each corresponding to the solder joint is. Located in the oral administration of the site can not be observed due to the expansion of A components of solder, it is necessary to use specialized equipment to bits. The BGA-3500-G optical alignment advantage of the plane mirror tilted to 45. The principle of reflection imaging through a camera head for precise alignment.
5 Hot air re-flow solder
Hot air reflow is the key to the entire repair process, of which the following questions:
1) chip rework to reflow the curve should be the initial welding curve close to the chip, hot air reflow soldering curve can be divided into four zones: the preheating zone, heating zone, the reflow zone, cooling zone, four-zone temperature, The time parameter can be set, connected to the computer these programs are stored and can be called at any time.
2) In the reflow soldering process is necessary to correctly choose the Sounds of the district heating temperature and time, should be noted that the heating rate. General. Before loo ℃, the maximum heating rate of no more than 6 ° C / s heating speed string 100 ℃ after no more than 3 ℃ / s. Cooling zone, the maximum cooling rate of not more than 6 ℃ / s,. Because of high heating rate and cooling rate are likely to damage the PCB and chip. The damage is sometimes can not be observed by the naked eye. Different chips, different welding tone, choose a different heating temperature and time. Re-flow temperature of the components, such as the reflow temperature of the ceramic BGA (the CBGA) components should be higher than the plastic BGA (PBGA,), 90Pblosn should be more 63Sn37Pb paste selection of a higher reflow temperature. No-clean solder paste, a lower activity than non-no-clean solder Xiao, welding temperature bean too simple, welding time should not be too long to prevent oxidation of the solder pieces to change.
3) hot air reflow the solder in the bottom of P which must be capable of being heated. Bottom heating purpose is twofold: to avoid the PCB, single-sided heat warpage and deformation, so that the solder paste melting time. Large size PCB rework BGA components, bottom heating is especially important. Heating mode at the bottom of the BGA-3 592-G rework equipment, there are two, one is the hot air heating, an infrared heating. The advantages of hot air heating is heated evenly, general repair process is recommended to use this heating; the shortcomings of the infrared heating PCB uneven heating.
4) to choose a good hot air reflow nozzle. Hot air stream and then spray is a non-contact heating, relying on high-temperature air heating
The flow of the solder joints on the BGA chip solder paste to melt at the same time. U.S. OK first invented this are the mouth, it BGA components sealed to ensure that the tax given temperature in the reflow process, and at the same time protect the adjacent components not proofread flow of hot air heating and damage.
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