Controllable factors of lead-free wave soldering process

Combining innovative quality methods with traditional design-of-experiments in lead-free wave soldering minimizes unnecessary variability, reduces production losses and delivers greater benefits. To achieve the goal in the best possible way, produce all products as possible with minimum deviation between products.

Controllable factors of lead-free wave soldering process:

In order to design a reasonable wave soldering process test, first list the problem, goal and expected output characteristics and measurement methods. Then determine all process parameters and define the relevant factors affecting the results:

1. Controllable factors:

C1 = factors that have a significant effect on the process and can be directly controlled;
C2 = The factor that needs to stop the process if the C1 factor changes.

In this process, three C1 factors were selected:

B = contact time
C = preheat temperature
D = amount of flux

2. The noise factor is a variable that affects deviation and is impossible or cost-effective to control. Changes in indoor temperature, humidity, dust, etc. during production/testing. For practical reasons, the noise component was not factored into the test. The main objective is to assess the contribution of individual quality influencing factors. Additional experiments must be done to quantify their response to process noise.

Then select the output characteristics that need to be measured: the number of pins without solder bridges and the qualification of via filling. Usually one factor at a time studies are used to determine controllable parameters, but this experiment used an L9 orthogonal array. In only nine trial runs, three levels of four factors were investigated.

Appropriate test setup will yield the most reliable data. The range of control parameters must be as extreme as practical to make the problem apparent; in this case, poor penetration of solder bridges and vias. To quantify the effect of bridging, the soldered pins without bridging were counted. Effect on through-hole penetration, each solder-filled hole marked as indicated. The maximum total number of points per board is 4662.