PTH孔金属化互联缺陷 ICD 测试评估方法

Test Vehicle and Procedure for Measuring ICD

With ICD remaining a concern for PWB quality, it is recommended that fabricators and end users alike consider periodic evaluations of the electroless copper process. Utilizing a simple test vehicle (that is designed to fail) is an excellent means with which to quantify the electroless copper process and its tendency to cause ICDs.

The solder shock (post separation) test vehicle (Figure 7) used for this comparison test is described and shown as follows:

* Panels are 140 °C T laminate and 1.6 mm thick with 1.20 mm holes. The panel is an eight-layer board with the n-1 layers 0.18 mm from the outer foil. A 1 oz. foil is used and the construction is typically unbalanced;

* Innerlayer integrity was measured at 7X and 10X sequential solder shock at 288 °C for 10 seconds per thermal shock; and

* To prevent additional stress, holes to be examined (Figure 8) are routed from the test vehicle. Inspection and observations are made on the prepared microsection before and after etching using ammonium hydroxide/hydrogen peroxide etchant.

This is a procedure that is highly recommended for any fabricator engaged in producing high reliability PWBs, especially those that are subjected to lead-free assembly. If one detects changes in the extent of failure recorded from the analysis, this should serve as a red flag that there are process issues that must be addressed. Keep in mind that this test vehicle is designed to fail. Essentially, as long as there is 5 percent or less of failed interconnects in the samples, it is

an indication of a fairly robust plated through-hole (PTH) process.