基于加热因子的回流曲线的优化与控制

回流焊形成的焊点质量与回流焊过程密切相关。基于加热因子Qη对回流焊接过程进行优化控制。根据焊点疲劳寿命随加热因子分布的特点,提出了对冷点加热因子取最优范围下限值控制策略(冷点代表回流过程中经历的加热因子最小焊点),以使所有焊点的加热因子尽可能都在最优范围之内。冷点下限控制策略满足了大部分焊点的高可靠性,而少部分超出最优范围上限的焊点的可靠性虽略微下降,仍可形成良好焊接。由于加热因子理论不对回流曲线形状做严格要求,定义了两个组合参数:形状参数Ht和移动参数Hb,对冷点的加热因子进行控制。并且根据统计学原理利用实验建立Qη与Ht和Hb的回归关系,发现Qη与Ht、Qη与Hb大体上成线性关系,其为Qη的预测和控制带来了极大的便利,从而使焊接可靠性易于得到保证。

Optimization and Control of Reflow Profile Based on Heating Factor

The quality of solder joints in SMT line is mostly dependent on reflow soldering process.In this paper reflow profile will be optimized on the basis of heating factor Qη,which determines the fatigue lifetime of solder joint.Long lifetime will be achieved with optimal range of heating factor.Let cold joint represent the solder joint experiencing the minimum Qη during reflow process.Then most other solder joints will experience optimal range of Qη while we make Qη of cold joint equal to the lower limit of optimal range of heating factor.Lifetime of some solder joints with highest temperature on the PCA are likely to be a little impaired if they are beyond the upper limit of heating factor.They are acceptable soldering yet according to lifetime distribution heating factor.Since it is unnecessary to pay particular attention to the shape of reflow profile according to heating factor theory,we can focus on realization of optimal range of Qη.Two combinatorial parameters Ht and are Hb defined and controlled to achieve the lower limit of optimal range of Qη corresponding to cold joint.And the experiments demonstrated that was linear with Ht and Hb respectively.Least squares estimation method can be used to building the linear regression model of heating factor with each of the two parameters.Thus it facilitates the prediction and control of heating factor.Optimization of reflow soldering process based on heating factor can be accordingly realized to guarantee high reliability of solder joints.