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The Reason and Common Solutions of Tombstoning for SMT Assembly 02
Jul 21, 2017

The result is that the smaller the component volume is likely to occur during the reflow process of CHIP components such as chip capacitors and chip resistors, especially in the production of 1005 or smaller 0603 patch components, In the process of reflow soldering of the surface mount process, the patch element will produce defects due to arrogance and desoldering. As shown in the figure, the image is called "tombstoning" (also known as "Manhattan" phenomenon.)."Tombstoning" phenomenon is due to the solder bumps at both ends of the solder plate in the reflow melting, the two parts of the surface of the solder joint surface tension is not balanced, pull the end of the larger components along the bottom Rotation caused by the tension caused by a lot of factors are not balanced, the following will be a brief analysis of some of the main factors.


3. Placement offset

In general, the component offset generated during placement is automatically corrected during the reflow process due to the surface tension of the solder paste when it is melted. We call it "adaptive", but the offset is serious and the pull Component erect to produce "tombstone" phenomenon. This is because: (1) more contact with the components of the solder end to get more heat capacity, which first melted. (2) the two ends of the component and the solder paste of the different viscous. So you should adjust the accuracy of the components of the patch, to avoid a larger patch deviation.


4. Thickness of solder paste

When the thickness of the solder paste becomes smaller, the phenomenon of the tombstone will be greatly reduced. This is due to: (1) thin solder paste, solder paste when the surface tension decreases. (2) solder paste thinning, the entire pad heat capacity decreases, the two pads on the solder paste at the same time the probability of melting greatly increased.


5. Weight of components

Because the solder paste produced by the tension is generally 1g to 3g or so, so the lighter component "tombstoning" the phenomenon of high incidence, the probability of occurrence is also higher; this is because the uneven tension can be easy Pull the components. Therefore, in the selection of components, if possible, should be preferred to the size of the larger components. There are many welding defects, this article lists only three of the most common defects. There are many measures to solve these welding defects, but often mutual restraint. Such as to improve the preheating temperature can effectively eliminate the monument, but it is possible because the heating speed becomes faster and produce a large number of solder balls. Therefore, in solving these problems should be considered from a number of aspects, choose a compromise.