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1、Date:08/30/2000Prepared by Andy Gan,COB Internal Training,What is COB?,CHIP ON BOARD,COB Flow Chart,COB Procedure,1.Clean PCB Clean spots which exists in PCB to assure dropping easily.,COB Procedure,2.Drop Red Epoxy Resin Use in fixing chip,quantity of glue shall be exact and well mixed.,COB Procedu
2、re,3.Mounting Chip Use vacuum pen to fix chip in PCB,notice polarity and shifting angle(5 degree).The air pressure is different from each chip.Vendor will adjust air pressure to the minimum at first,then raise it slowly to fit the requirement.4.Bake Solidify epoxy resin by bake-box,fix chip.,COB Pro
3、cedure,5.Wire bonding Connect welding dot of chip and tin-foil in PCB by aluminum line.Effecting factor of wire bonding:a.Wire diameter b.Angle of welding c.Welding dot d.Tensile force of aluminum line,Effecting factor of wire bonding,a.Wire diameter Aluminum line has C.C.C,K.S and TANAKA,and diamet
4、er include 1.0 mil and 1.25 mil.Select 1.0 mil if distance of welding dot is little and thickness of PCB is big.Select 1.25 mil if distance between welding dot of chip and tin-foil in PCB,this also ought to fit the condition that the distance of welding dot is large and small thickness in PCB.,Effec
5、ting factor of wire bonding,b.Angle of welding must be less than 45 degree Corrective action if the angle is large than 45 degree 1.Rearrange the position of golden finger.2.Prolong finger which be in“2”.,Effecting factor of wire bonding,c.Welding dot Minimum size of golden finger is 6 mil and minim
6、um of distance is 6 mil too.Notice:The above welding dot minimum size is accuracy of FR4 glass fiber sheet.The requirement cant be realized if it is CAM3 cardboard.,Effecting factor of wire bonding,d.Tensile force of aluminum line(1)PCB hasnt been cleaned complete It will be difficult to weld alumin
7、um line if you dont remove the spot from PCB.(2)Parameter of machine set up not correctly New models machine parameter is set up by technical personnel according to their experience.They have to observe the working condition,analyze the root cause of defect,and confirm the parameter.(3)Material fact
8、or*Width of golden finger is too little,welding shift,result in tensile force reduce.*Surface of golden finger dont be dealt well.*Deformation of PCB.*The nickel-plated layer of welding dot in chip.,COB Procedure,6.Process Test Test short-circuit,cut-circuit,non-welding etc by microscope.Test tensil
9、e force of aluminum line by force gauge per 2 hours.,7.Function Test Test welding dots short-circuit,cut-circuit,non welding by test tools.Any defect will be maintained.,COB Procedure,COB Procedure,Comparison between conductive rubber and probe:,Function test means to test the function of the produc
10、t with the electrified PCB by testtools.Some non-welding components will be fixed on tools.But the covering rate willbe involved generally,which mean the testing result cant cover the all function of theproduct.,COB Procedure,Maintain defects:1.Dont scrape the chip and leave the dregs between two we
11、lding dots when you are maintaining with a needle pen.2.Welding power ought to be 5 units more than normal and the pressure ought to be 2 or 3 units more than normal.3.Control the time of washing black glue,or the aluminum line will be broken.,COB Procedure,8.Encapsulate:Prevent the welding-line fro
12、m being damaged during the shipping.For example:(HYSOL EO1016)HYSOL EO1016 is a unique one component epoxy encapsulant with excellent shelf stability,flame-out and fast curing capability at moderate temperature.It is intended for applications requiring excellent handling properties.Recommended Cure2
13、 hrs150(302)Alternate Cure16 hrs93(199)Note:It should not be used for casting masses larger than 50 grams.,COB Procedure,9.Function Test Test if there was any defective symptom during the course of encapsulate.10.Bake Solidify black glue to protect the chip.11.Function Test Test if there was any def
14、ective symptom during the course of bake.12.PQC Test appearance of black glue,such as core hole,square and height of black overlap glue.,Equipment Introduction,Supplier:ASMModel AB510X-Y workstation process:50 x50mmAccuracy of component placement:5um(0.2mil)/step(motor step)workstation:max.size of P
15、CB 130 x170mmAccuracy:0.225/stepZ process:10mm(0.4”)Accuracy:12.7um(0.5mil)/step(motor step)Wires:350 slips/PCBChips:5 pieces/PCBMethod of wire bonding:Ultrasonic wareDiameter of wire:1.0mil 2.0mil(0.025mm 0.05 mm)Pressure of wire bonding:15 100g,Output angle:30Welding speed:3.5 slips/secondAccuracy
16、 of wire bonding:0.02mmRange of welding:100mm from chip to PCBs further endWire distance:within 4 mm(no more than 5mm)Note:Five percent bad rate will be increased per.more 0.5mm wire distance if the wire distance is outran standard(4mm).,Equipment Introduction,Requirement of PCB,1.Width of golden fi
17、nger PAD:4mil2.Width of chip PAD:3mil3.Distance between golden finger:4mil4.”+”sign must be designed on PCB to proofread the chip position,and it should be near the golden finger.5.Try to reduce quantity of prevent-welding paint at the position of black glue,this can combine the black glue tightly with PCB.6.Prevent PCB deformation which can damage chip.,1.2mm,0.5mm,
