用了underfill胶的BGA如何维修？

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?准备工作/Equipments needed：
–加热装置(维修工作台/热风枪)
  HeatingEquipment(Rework Station/Hotair gun)
–头部楔形的小木棍/牙签
  Smallwood stick with cuspidal end or toothpick
–助焊剂/Flux
–棉签/Cottonstick
–尖头镊子/Nipperwith cuspidal end
–吸锡带/焊锡丝/Solder wick and solder wire
–若有可能的话加上显微镜/Microscope if possible

?加热/Heating：
–设置热风枪温度到150℃热风枪加热PCB板的BGA区域
  Setthe temp to 150℃, then heating the BGA area
  of the PCB with hot air gun
–若用维修工作台可设置温度值在150℃
  150℃ temperature setup is suggestion if use
  rework station
–温度不要超过焊球熔点
  Never exceed the solder ball melting point

原因/Why：
–underfill在加热到100℃左右时会变得较软，容易去除
  It’seasy to remove softened underfill above 100℃

–超过焊球熔点后，去胶时易把周边小元件碰掉
  Toohigh temperature may cause small component
  around BGA be removed;

?去周边胶/remove the underfill around the BGA：

–在基板底部使用热风，加热至100C左右,在此状态下可使用尖锐木制工具（如牙签等）去除元器件周围的胶粘剂。
  Heating PCB to 100C-150C, remove underfillaround the BGA with wood stick (eg. Toothpick)
–在此状态下，焊锡尚未熔化，不会影响周边靠得较近的元件
  Small component around BGA will never beremoved because the temperature is lower than the melting point
–或者使用带温度的尖头烙铁直接去除芯片周边的胶（这需要较熟练的维修人员）
  Or you can remove the underfillaround BGA with cuspidal iron tip directly (this operation onlyfor  the professional rework operator )
?原因：–分离芯片与周边器件的胶连接
  Divide the BGA from the components around it
–保证芯片能被轻松卸下而不损及周边器件及PCB板
  To be insured that the BGA will be removedwithout damage to the component around it.


?加热/Heating：
–调整热风枪加热温度至BGA焊球熔点以上（如350C）
  Adjust the hot air gun’s heating temperatureto above the melting point of solder joint（eg.350C)
–保持一定时间以保证焊球熔化，不要加热太长时间（正常小于1分钟）
  Keep some time to melt the solder ball, buttoo long time is not suggested
–维修工作台可以设置温度曲线（具体要根据实际相应调整）
  You can setup a profile if use rework stationaccording to the test result
–在保证焊球熔化的前提下温度尽可能低点
  Set low enough temperature if the solder ballcan be melted in one minute
?原因/why：
–使焊球熔化以取下芯片
  Melt the solder ball to remove the BGA
–过快温度上升/过高温度/过长时间加热会对PCB板造成损伤
  Too fast temperature ramp up/too hightemperature/too long heating time may do damage to PCB and components;


取BGA

–到芯片卸下时间点，使用金属镊子在芯片一角轻撬芯片，并将芯片从基板分离

  Righttime to remove, we can prize the BGA from one corner with cuspidalnipper

–只要加热至BGA下焊球熔化，此时即可撬下芯片而不会损坏PCB板，胶在>100C时已变软，很容易取下

  Onlysolder ball was melted, BGA can be remove without damage to PCB, because theadhesive is softened when the temperature is higher than 100C.

?清除残留焊锡/remove the solder residue：–加助焊剂

  Putthe flux on PCB with the residue of adhesive and solder

–用烙铁加吸锡带尽量清除PCB板上残留的的焊锡

  Toremove the solder residue with solder wick and iron

–?原因/why：–使焊盘表面光滑无毛刺，在去残胶时不易带起焊盘

  Tosmoothen the surface of the Pads, then the Pads will be not easy to be removedwhen we clean the adhesive residue on PCB

––注意/Attention：

  千万小心，不要损及PCB板上的焊盘

  Be carefully, don’t do damage to the Padson PCB

去残胶 /Removethe adhesive residue
?在显微镜下用加热器加尖头镊子清除残胶/use heating equipment + cuspidalnipper to clean the adhesive residue under the microscope–用棉签涂助焊剂于PCB上残胶处

  Put the flux on the adhesive residue withcotton stick

–设置热风枪至150C，加热PCB上的残胶

  Heating the adhesive residue with the 150C hotair

–用尖头镊子小心去除残胶

  Remove the adhesive residue with cuspidalnipper carefully

–?原因/why：–助焊剂可以在一定程度上帮助残胶软化

  Flux may soften the adhesive under hightemperature

–温度越底，PCB板所受的热冲击越小，焊盘强度越大

  Lower temperature under melting point can keepthe pull strength of Pad

?当PCB板上有较多的被刮下来的残胶时，可能会影响视线，可用棉签清理一下

  Whentoo much removed adhesive stay on the PCB may affect the view, you can cleanthese with cotton stick

?然后再在显微镜下检查一下焊盘上的锡是否有毛刺等，可能会影响去胶时把焊盘拉脱，如有的话，涂点助焊剂，用烙铁清理一下，使焊盘表面光滑。

  Checkthe Pad, coating flux and smoothen the solder surface on the Pad if there areburr on the Pad, or the Pad may be pull down during the adhesive cleaning.

?然后再返回上一步，继续在显微镜下用尖头镊子去残胶

  Backto the previous step, continue to clean the adhesive residue with cuspidalnipper under the microscope

?焊盘上锡/tin the Pads：?–用烙铁和锡丝给焊盘再上锡(滚锡),保证焊盘上无残胶或其它杂质污染,均匀上锡

  Tinthe Pads to confirm there is no residue on the Pads

–?原因/why：–保证BGA再次安装后，芯片底部无杂质影响再次underfill

  Tobe insured that the BGA can be underfilled again after re-assembly

–滚锡以验证焊盘上无污染

  Tinthe Pads to check there is no residue polluted

?重新焊上新的BGA/ BGA Re-assembly–加助焊剂于PCB上

  Put the flux to the PCB

–按正常换BGA程序安装新的BGA

  Re-assemblingthe BGA according to the normal process

总结
?去周边胶/Remove the adhesive around the BGA?
---à卸芯片/Remove the BGA?
---à涂助焊剂/coating flux?
---à去残锡/Remove the soldering residue?
---à去残胶/remove the adhesive residue?-
--à涂助焊剂/coating flux?
---à滚锡/tin the Pads?
--àBGA重装/BGA re-assembly、




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本文整理自《underfill维修指南》百度文库，作者：henkel『本文转载自网络,版权归原作者所有,如有侵权请联系删除』