Underfill 维修指南

Rework Process

Dispense & Cure Underfill

Remove Defective Component

Clean Pad Site

The Typical Profile for SAC AlloyTop Nozzle Heater 3000C Bottom Heater 2000C TC-1 1000C TC-2 TC-3 100 s 200 s 300 s 400 s 500 s

Recommended DT of (TC-1,2 3) within 10oC2

Remove solder and underfill residue

Proper Substrate Cleaning

Excessive Pressure / Time

Rework Guidelines 准备工作/Equipments needed:– 加热装置(维修工作台/热风枪) Heating Equipment(Rework Station/Hotair gun) – 头部楔形的小木棍/牙签 Small wood stick with cuspidal end or toothpick – 助焊剂/Flux – 棉签/Cotton stick – 尖头镊子/Nipper with 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

Rework Guidelines —adhesive around the BGA (fillet)

Remove the

加热/Heating: – 设置热风枪温度到150C热风枪加热PCB板的BGA区域 Set the temp to 150C, 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150C 150C 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100C左右时会变得较软，容易去除 It’s easy to remove softened underfill above 100C – 超过焊球熔点后，去胶时易把周边小元件碰掉 Too high temperature may cause small component around BGA be removed;6

Rework Guidelines —

Remove the adhesive around the BGA (fillet)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 underfill around 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 be removed 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 underfill around BGA with cuspidal iron tip directly (this operation only for 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 removed without damage to the component around it.7

Rework Guidelines -- Remove the BGA 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 temperature to 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, but too 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 station according 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 ball can 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 high temperature/too long heating time may do damage to PCB and components;

Rework Guidelines -- Remove the BGA

Rework Guidelines -- Remove the BGA 芯片卸下/Remove 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 Right time to remove, we can prize the BGA from one corner with cuspidal nipper – 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 Only solder ball was melted, BGA can be remove without damage to PCB, because the adhesive is softened when the temperature is higher than 100C.10

Rework Guidelines --Remove the BGA– 检查卸下芯片的焊球/inspect the solder ball of BGA removed: 加热温度不够，或卸芯片不及时 Heating temperature is not enough, or it’s too late to remove the BGA, solder balls were solidified again

加热不均匀，局部地区温度不够或卸芯片不及时 Heating is not good, some area’s temperature is not enough, or it’s too late to remove the BGA

加热温度足够 Heating is enough

Rework Guidelines -- 去残锡/remove the solder residue 清除残留焊锡/remove the solder residue: – 加助焊剂 Put the 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 To remove 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 To smoothen the surface of the Pads, then the Pads will be not easy to be removed when 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 Pads on PCB

Rework Guidelines -- 去残胶 /Remove theadhesive residue 在显微镜下用加热器加尖头镊子清除残胶/use heating equipment + cuspidal nipper 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 with cotton stick – 设置热风枪至150C,加热PCB上的残胶

Heating the adhesive residue with the 150C hot air– 用尖头镊子小心去除残胶 Remove the adhesive residue with cuspidal nipper 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 high temperature – 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 ke

ep the pull strength of Pad13

Before cleaning

After cleaning

Rework Guidelines -- 去残胶 /Remove theadhesive residue 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 When too much removed adhesive stay on the PCB may affect the view, you can clean these 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。 Check the Pad, coating flux and smoothen the solder surface on the Pad if there are burr 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 Back to the previous step, continue to clean the adhesive residue with cuspidal nipper under the microscope

Rework Guidelines -- 焊盘上锡/tin the Pads 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 Tin the 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 To be insured that the BGA can be underfilled again after re-assembly – 滚锡以验证焊盘上无污染 Tin the Pads to check there is no residue polluted

Rework Guidelines -- BGA安装/BGA reassembly

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-assembling the BGA according to the normal process

Rework Guidelines -- 总结/Summary

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

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