Optimising the necessary amount of solder paste for Pin-in-paste technology

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Dr. Krammer Olivér
Department of Electronics Technology

Nowadays only a few through-hole components can be found on a printed circuit boards (PCB), but the soldering of those is necessary too. That is why selective soldering methods come into view; however they can be complicated and resource-demanding. That is the main reason of the continuous developing of the Pin-in-Paste technology.

To make this process defect-free, the most important step is to apply the right amount of the solder paste to the PCB with stencil printing. Besides to avoid defects, we have to make an accurate calculation of the paste amount. The commonly used expression for calculating the amount of the paste deals with rough approximations. That is why I decided to review this explicit expression.

In the first part of my thesis, I introduce the steps of the reflow technology and the Pin-in-Paste technology based on literature survey. I also present different calculating methods to determine the necessary amount of the solder paste, and I presented in detail the method I applied.

In the second part of my thesis, a new method is presented for calculating the right amount of solder paste for Pin-in-Paste technology for through-hole components. I used the Surface Evolver liquid profile-modeling software to make the model of the ideal shape for the through-hole solder joints.

I calculated the volume for different solder joints (for round and square shaped pins) with the explicit expression. Then I compared them with the volumes obtained from the modeling software. Based on this comparison, I determined correction factors for different lead geometries and for different hole diameters and solder ring widths. Using this correction factors, I made test soldering. After that, I examined the solder joints. When I used the volumes from the explicit expression the wetting of the contact ring was insufficient. Based on X-ray photographs, there were less voids and wetting failures with those joints where I used volumes from the modeling software. At last, I made cross-sections to demonstrate the different type of the soldering defects.


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