THR Printed Circuit Board Layout and Template Design

We recommend the following printed circuit board layout for our COMBICON and MINI-COMBICON male connectors:

Starting with pins with a square cross section, the inside diameter dI of the plated-through drill hole should be approximately 15 to 22/100ths greater than the pin diagonal. This difference takes into account the corresponding process tolerances of the components and fitting accuracy of the pick-and-place systems.

The following factors must also be taken into consideration after determining the diameter of the hole. The design of the pad geometry is affected by:

• The required air and creepance distances,
• The minimum requirements placed on the soldering point, e.g., to form appropriately strong solder menisci.

The component design also plays a role here. If the component contour is moved over the desired pad geometry, it must be adapted to the available space under the component to prevent the solder paste from coming into contact with the housing and to ensure optimum access for heat to the soldering point.

Of course, the design of the template is directly linked with the design of the solder pad. The thickness of the template is of particular importance here. When integrating THR components, it is not necessary to modify all or even part of the template thickness for the THR drill holes. Modifications are unnecessary even if template thicknesses of 120 µm or even 100 µm are used in the future. The template thickness is not a decisive factor when making up solder paste; what is important is the correct filling of the drill hole and pushing through the desired amount of solder paste, as will be illustrated later.

The geometric form must once again be considered. We have a plated-through drill hole with an inside diameter dI, an appropriately selected outside diameter dA, and now a customized template cutout with a diameter dS. For COMBICON with a dI of 1.45 mm (0.057 in.) the outside diameter dA is correspondingly 1 mm (0.039 in.) greater, taking into consideration the residual ring R for which we recommend approximately 0.5 mm (0.020 in.). R = 0.5 mm (0.020 in.) is only a recommendation. Often only a smaller residual ring can be used due to the design. In terms of process technology this is not a problem, however it leads to smaller solder menisci and is therefore somewhat harder to determine. However, it is important that the template hole is now always at the edge of the pad. Applying excess pressure is not recommended. Excess pressure refers to pressure applied in addition to the solder pad ring, sometimes even through to the solder resist. We recommend a template cutout that corresponds to the outside diameter of the drill hole minus 1/10 mm.

The risks associated with excess pressure or insufficient pressure on the solder paste under the template should be emphasized again.

If the template always contacts with the pad, little or no solder paste can get in between the pad and the solder resist or under the template. This means less smearing of the solder paste occurs and thus fewer cleaning cycles are required.

The situation is different if the template cutout is larger than the solder pad. In this instance, solder paste can get on the solder resist and under the template. This results in heavy smearing and thus frequent cleaning cycles. There is also a danger of soldering globules forming after the reflow process and a risk posed by the reduction of air and creepance distances on the printed circuit board.