Hunan,



There are  three type of process but depending on the type of components



1. If no BGA / CSP , fine-pitch QFP, fine-pitch IC etc,



Top side - SMT



bottom side - Wavesoldering





2. Reflow both top and bottom side SMT component together





3. Reflow the bottom side SMT first and then reflow the top side SMT at

second reflow





For the process of 2 and 3, the weight of the component and no. of

soldering point per component is important to know for the bottomsided

reflowed component in preventing its dropping at the second reflow.



Typically, use the same solder paste in the same alloy if the component at

the bottomside is light enough.  If  the presence of heavy component with

less soldering points at the bottom side, there are several ways to cope

with it



1. Lower the peak temperature at the bottom side (Set  the bottomside

preheator lower comparing to topside preheator)



2. Use the pallet to cover the heavy component



3. If the variation for standoff of the bottomside component is not much,

place the board at mesh instead of rail to pass



4. Apply red glue to hold the heavy component at the bottomside when

passing the second reflow



Regards,



Jackson Chan



Technical Services Manager

Cookson electronics - Alpha Metals





                                                                           

             huanan_6230                                                   

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             2008/01/10 下午           [TGA] 双面贴装                      

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请教各位：





      双面纯贴装工艺的板子，是否必须过两



次回流，前后用两种温度不同的焊膏呢，还是



用一种焊膏直接过一次回流即可，这样是否会



对焊接质量或元件本身造成损害？谢谢赐教！







                  中国通号公司  张桦楠









惊爆：满300直减150元，就这个价! vancl特价促销