This is a re-post / clarification of a question I posted previously.

I would like to know what others consider an ideal topside 
laminate board temperature during preheat (using bottomside preheaters only). 
The "rule of thumb" we have been using is that we want this to be between 190 
and 220 F (measured using a Wave Solder Optimizer and/or tape dots). We are 
using an alcohol-based water soluble flux and standard tin/lead solder at 495 F.

I got back several replies previously stating that I should just go by the data 
sheet for the flux I'm using. Several people also pointed out that the 
temperature of my board will vary with board mass, and be different from the 
temperature shown by the Wave Optimizer. However, let's assume for the sake of 
this discussion that my flux is active throughout a temperature range quite a 
bit wider than this, and that the Wave Optimizer accurately reflects the actual 
board temperature. 

What I want to know is, assuming the flux has done it's job, what's the 
recommended temperature, from a solderability standpoint, that my board should 
be at before it actually hits the solder wave? Should I try to get it as hot as 
I can without destroying components? If, for example, all of my components are 
supposed to withstand 250F for several minutes, should I aim for a 250F 
temperature? What are the considerations here? Should I be trying to minimize 
the difference between the board temperature and the solder wave temperature? 
What actual measured board temperatures are others using?

Thanks,

V. Chapman 








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