BGA pad tilt occurs for many reasons. Because these elements pads located below the line of sight beyond repair technician, the technician can not see these solder joint, which may melt before all the solder connection point trying to move elements. Similarly, due to excessive heating of the bottom or top surface, the temperature is too high or the heating time is too long, BGA pads may be excessively heated. As a result, since the operator may want to make all of the BGA pads are melted and the overheating in the region. Too many or too little heating may produce the same unpleasant results.
A position repeatedly rework may also cause the pad to the circuit board layers lose adhesion. In the solder reflow temperature, SMT pads are fragile because the bonding pads of the board is. BGA is a strong element of PCB connection strong; the pad surface area is also worth noting that, when melted, the maximum surface tension of the solder.
In many cases, regardless of the most skilled operators to use its best efforts, BGA repair accidental tilt pad may still be seen. what should you do?
The introduction of new dry film, rubber-soled pads. The new pad is to use a specially designed press to bond the adhesive to the surface of the PCB. You must make the board smooth. If the substrate material damage, must fix with another program. This method is used to replace copper foil BGA pads, dry film for plastic substrates. Proceed as follows.
• Clean the area to be repaired
• Remove the pads and short connection failure
• use a knife to scrape gum residue, stain or burn materials
• scraped solder or coating on the wires
• Clean the area
• Connect the board area apply a small amount of liquid flux, and tin. clean. Lap length should be less than twice the solder connection wiring width. Then, you can connect the new BGA pad inserted via holes in the original BGA pad. The solder resist is removed via holes, appropriate treatment. The new board of the pad area must be smooth. If you have inner fiber is exposed plate, or the surface of the deep scratches, it should be repaired. BGA replacement pad height is critical, especially for eutectic solder ball elements. Remove the BGA pad or wiring board with a solder material between the vias, in order to maintain a low profile. If necessary, slight wear into the board in order to ensure a high degree of connection does not interfere with the replacement of components.
• Choose a BGA replacement pads, with the closest to replace the pads. If you need special size or shape, it can be user customized. These new BGA pads are made of copper foil, tin foil top surface, a bottom surface have cemented glue sheet.
• Before trimming the new pad and carefully scrape off the solder connection point area on the backside of the new pad glue cement sheet. Only scrape the resin substrate from the solder joint area. This will allow the exposed weld area. When dealing with replacement pads, or other material to avoid finger contact with the resin substrate, which may contaminate the surface and reduce the bond strength.
• Cut and trim the new pads. Tin cut from the edge, cut the length of stay to ensure maximum permissible welding wires lap.
• put new pads on the top surface of a heat tape, the new pad into position on the surface of the PCB, with tape to help positioning. During the adhesive tape remain in place.
• select suitable for a new shape of the bonding pad tip, the tip should be as small as possible, but it should completely cover the surface of the new pads.
• Positioning PCB, to make it smooth. Gently heat the tip on the pad cover on the new tape. Applying pressure according to the manual repair system is recommended. Note: too much pressure may cause the adhesive spots PCB surface, or cause new slide pad position.
• After the timing bonding time, lift the iron, remove the tape for positioning. Pads completely refurbished well. Carefully clean the area to check whether the new pad properly positioned.
• dip a small amount of liquid flux to weld the overlap area connection, the connection to the new welding pad on the PCB surface line. As far as possible with a minimum of flux and solder to ensure a reliable connection. In order to prevent excessive solder reflow can put tape on the top surface of the new pads.
• mixed resin coated welding wires lap. Curable resin. With a maximum recommended heating time to ensure that the highest bond strength. BGA pad normally lasts one or two reflow cycles. Also in the new pads can be coated with resin around to provide additional bond strength.
• Apply the required surface coating.
After the repair pad, visual inspection should be done (including the new width and spacing pads), electrical connections and measure. The results of this procedure is to be repaired and a PCB, a PCB and thus less trash, the "bottom line (bottom line)" make a positive contribution