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1、No-clean LEAD FREE Solder Paste Lead Free SOLUTIONS you can TRUST Challenging New Technologies Sep. 04, 2006 - Towards Higher Solder Joint Reliability - Development of Anti-Hidden Pillow Defect Lead FreeLead Free solder paste 2 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright
2、 (C) 2006 Koki Company Limited. All Rights Reserved. Content Potential cause of Hidden pillow defect Mechanism of occurrence of Hidden pillow defect Key words to cope with Hidden pillow defect Enhancement of heat resistance Enhancement of wetting reaction speed Hidden pillow defect test with BGA Sum
3、mary 3 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki Company Limited. All Rights Reserved. Potential cause of Pillow defect 1.Excessive OXIDATION of BGA bumps during heating process 2.EXHAUSTION of flux activation Disrupt merger of BGA bump with molten solder
4、 SEPARATION of BGA bumps from solder paste 4 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki Company Limited. All Rights Reserved. Cause of separation of BGA bump from pasteCause of separation of BGA bump from paste PrinterChip placerReflow Mounter Warpage of s
5、ubstrate Inconsistent bump size Inaccurate x-y placement Insufficient down-stop Inadequate temperature profile Warpage of component, PC board Lifting of BGA bumps due to wetting force Package Insufficient solder paste Inaccurate registration Print accuracy 5 CHALLENGING NEW TECHNOLOGIES Lead free SO
6、LUTIONS you can TRUST Copyright (C) 2006 Koki Company Limited. All Rights Reserved. Mechanism of occurrence of pillow defectMechanism of occurrence of pillow defect 1. BGA bump starts to be oxidized 2. Flux starts to be oxidized 1. Flux bleeds out. 2. Further oxidation of bumps. 3. Flux activation i
7、s consumed as solder melts. 1. Flux activation is consumed as solder melts. 2. Oxide film on bump surface and flux layer with almost no activation retards merger between bump and solder. 3. TAL is also limited. 6 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki
8、Company Limited. All Rights Reserved. Key words to cope with pillow defectKey words to cope with pillow defect Heat resistance of flux medium 1. Protect BGA bump and solder powder from oxidation. 2. Sustain activation strength for long time at high temperature environment. Increase wetting reaction
9、speed 1. Reduce exposure time of BGA bump. 2. Secure sufficient time for bump to collapse and merge with molten solder. Secure complete merging 7 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki Company Limited. All Rights Reserved. Enhancement of heat resistanc
10、eEnhancement of heat resistance Observe influence upon wetting performance due to high pre-heat condition. Solder paste :1. Conventional no-clean lead free paste (Sn3Ag0.5Cu) 2. Newly developed S3X48-M406-3 Stencil : 0.12mm thickness, 100% aperture to pad size Pad :0.35mm dia. BGA pattern PCB :FR-4,
11、 OSP finish, 100L x 100W x 1.6Tmm Reflow oven :100% hot air convection, 5 pre-heat zones, 2 peak zones Reflow profile : 0 50 100 150 200 250 300 0100200300 Teim (sec.)sec） Temperature (C) 200C x 100sec. 8 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki Company
12、Limited. All Rights Reserved. Conventional solder pasteS3X48-M406-3 Enhancement of heat resistanceEnhancement of heat resistance Due to flux spreading and excessive oxidation, solder particles of conventional lead free solder paste did not melt, while S3X58-M406-3 exhibited complete melting and coal
13、escence. 9 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST Copyright (C) 2006 Koki Company Limited. All Rights Reserved. Enhancement of heat resistanceEnhancement of heat resistance Observe influence of progressive oxidation of flux/molten solder over retention of flux activation. Sol
14、der paste :1. Conventional no-clean lead free paste (Sn3Ag0.5Cu) 2. Newly developed S3X48-M406-3 Stencil : 0.12mm thickness, 100% aperture to pad size Pad :0.8 x 0.8mm chip pad Solder ball :Sn3Ag0.5Cu, 0.76mm diameter PCB :FR-4, OSP finish, 100L x 100W x 1.6Tmm Test procedure :Melt solder paste on h
15、ot plate and drop solder ball at every 20sec. Solder ball Solder paste PC board Hot plate If flux is still active Complete merging If flux has lost activation Ball does not merge Oxidation and consumption of activation continue 270C 10 CHALLENGING NEW TECHNOLOGIES Lead free SOLUTIONS you can TRUST C
16、opyright (C) 2006 Koki Company Limited. All Rights Reserved. Enhancement of heat resistanceEnhancement of heat resistance S3X48-M406-3 Conventional solder paste Partially mergedMerged completelyMerged completelyMerged completely No mergePartially mergedMerged completely 60sec.40sec.20sec. after melting Immediately after melting Heating time Conventional paste was not able to merge with the ball only after 20
