I do not have any fixed guidelines except to say that this is essentially a volume calculation. If you know the size of the pin and the hole; then, it is a simple calculation for the volume of metal to fill the hole.

Furthermore, you need to allow for a fillet (I use 20% as a rule of thumb) to get the volume of metal you require. You will then need to double this because solder past is only approximately 50% by volume. This will give you the volume of paste you need to apply. A 1.6mm thick board will probably require a step stencil to get sufficient material deposited to fill the barrel.

A further point is that if you simply fill the barrel with paste much of this will get pushed out when you insert the component; usually this will drip off the pin prior to reflow. It is often advantageous to put a bar across the center of the hole (typically about 30% of the diameter), this forces the paste down the edges of the barrel and reduces the tendency for push through.

The Department of Systems Science & Industrial Engineering of the State University of New York, Binghamton and the Surface Mount Technology Laboratory of Universal Instruments Corporation did an extensive study on the pin-in-paste process using a DEK screen printer and Vitronics Reflow oven.

For more information on "Solder Paste Tests for the "AART" Process" (http://bit.ly/8YzhU2) you can contact George Westby, Director SMT LAB for Universal Instruments, at westby@uic.com. He is one of the authors of the report. Jeff Schake from DEK is also a great contact for this process, he can be reached at jschake@dek.com

In order to calculate the volume of solder paste needed, you will first have to calculate the volume of the pin then the volume of the plated-through-hole (PTH). Subtract the pin volume from the PTH volume.

This will give you the volume of solder needed. Additionally, you have to remember that the volume of the paste deposited has to be double the volume required to fill the solder gap. Stencil aperture design is also important for pin-in-paste applications.

A split aperture design stencil should be used if possible. A printed disc over the PTH will lead to inconsistent volumes as some of the solder paste will randomly fall out of the bottom side during the insertion of the lead.

A split print with a gap just large enough to make some minimal contact with the pin will yield a more consistent fill. On large fills AIM has been successful with prints up .250 inches distance from the edge of the PTH to the outside of the print. These will wick consistently down the PTH.

I have a Through Hole stencil design guideline that we use to make stencils for intrusive reflow stencil customers. Input data is 1-board thickness, 2-pin dimensions, 3-diameter of through hole, 4-dimensions of annular ring.

From this data we will calculate paste volume required to achieve positive fillets and design the stencil.

Three possible stencil designs are possible depending on paste volume required: Overprint apertures with single thickness stencil; Overprint apertures with step-up stencil; Two-Print Stencil. I have a recent paper on Intrusive reflow of Lead-free paste. Get in touch if I can help with your requirements.

Many applications, using a solder preform in conjunction with solder paste is an easy fix to achieve 100% hole-fill. These preforms come in standard pick & place shapes- 0603 / 0402 and are packaged in tape & reel. Look at http://www.indium.com/solderfortification/

Process: Print paste, Place preform by offsetting it away from the hole; place through-hole component; reflow

Based on the PCB & connector dimensions, it is possible to calculate the volume of solder needed to form a reliable joint and hence the volume of solder paste needed - pls email me at kvijay@indium.com and I can send the calculations. We have developed a spreadsheet to calculate the optimal stencil aperture dimensions based on the PCB & connector dimensions

• Use an optimized flux chemistry to maximize solder paste transfer and minimize paste trapped in the stencil apertures
• Using tapered connector pins to minimize the paste volume pushed out from the PCB hole
• Overprinting (typical is 10%) on the annular pad; this is also a function of the connector pitch and spacing available and ability of the paste flux to pull back solder during reflow