Thanks Tonny's advice.

 Stencil thickness is 4mil, 1:1开（0.3*0.38），倒0.05圆角 ;  the non-0201 components  solder joint is wetting;  indium SAC305; PCB immersion gold.


Best Regards
Cony Su

-----Original Message-----
From: TGAsia [mailto:[log in to unmask]] On Behalf Of Tonny Tong
Sent: Tuesday, July 29, 2008 11:19 AM
To: [log in to unmask]
Subject: Re: [TGA] 葡萄珠现象

Hi Cony:

it is really a concern at solder joint reliability. We do have same kind of experience at 01005, we have developed the process successfully without N2. It is definitely due to oxidation during reflow. Reason is that even the thickness of oxidized solder paste is same as like 0402,0603, but the percentage of oxidation is much higher than them for 01005 since the pad size(solder paste area) is much smaller. A solution is to reduce the time from 180 to peak temperature and lower down the time above liquid. If you can have ramp up rate at 2.5 degree c /sec from 180m to peak, that will be preferred. This is to minimized the flux consumption during reflow. This is the key for 01005 assembly. If this still can not solve the issue, N2 is the last solution for you and it is the most effective solution.

By the way, what is the stencil thickness and aperture size? What are there other components in the PCBA except 01005? Which solder paste was used? Surface finish?



-----Original Message-----
From: TGAsia [mailto:[log in to unmask]] On Behalf Of Jackson Chan
Sent: 2008年7月29日 10:49
To: [log in to unmask]
Subject: Re: [TGA] 葡萄珠现象

Cony,

For 0201 / 01005 pad, the quantity of the paste applied is quite small and result that the flux amount available is considered less.  Besides, it is the area where the hottest point exist so that the degree of flux exhaustion would be more significant than other components.  If the flux is exhausted significantly during the soak, the powder cannot completely melt together as shown in the photo provided.

Here is my suggestion

1. Try the short profile expecially in the temperature region between 150 -
217 deg. C

2. If the high soak is needed for your assemblies, you may need to find the paste which can withstand the hot soak.

Jackson Chan
Cookson Electronics - Alpha Metals (Hong Kong)

Low cost, high reliable alloy - SACX0807


                                                                           
             Cony Su                                                       
             <Cony.Su@TTELECTR                                             
             ONICS-IMS.COM>                                             To 
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                                                                   Subject 
             2008/07/29 上午           [TGA] 葡萄珠现象                    
             10:18                                                         
                                                                           
                                                                           
             Please respond to                                             
               Asia Committe                                               
             Task Group Forum                                              
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                  Cony Su                                                  
             <Cony.Su@TTELECTR                                             
              ONICS-IMS.COM>                                               
                                                                           
                                                                           





各位IPC专家大家好：
    现在有一个问题想向大家请教一下：由于现在的一些小的表面贴装元件（比如
0201，01005等）已经进入了量产阶段，随之也产生了一个新的问题：葡萄珠现象。就
是在无铅工艺中，从回流焊出来的小的元件焊点上的表面看起来有很多颗粒状锡
珠，像锡膏未融，又像冷焊，但是做切片后，它又是完全焊好的。供应商分析那些焊
点表面颗粒是氧化了的锡粉由于在回流中助焊剂被过早的挥发掉了。IPC-A-610标准里
对此现象还没有定义应是可接受还是拒收条件。不知道在做的同行是否碰到类似的问
题。现在我们已经尝试更换多种锡膏，调试profile，扩大钢网孔径等方法，效果已有
很大改善，但是葡萄珠问题仍然存在。


Best Regards
Cony Su
 [attachment "graphing.jpg" deleted by Jackson Chan/AlphaMetalsHK/Cookson] [attachment "Cross section of joint with graping.jpg" deleted by Jackson Chan/AlphaMetalsHK/Cookson]

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