Bob Willis presented this paper and exhibited at Productronica in 2001

Pin-in-hole, intrusive, pin-in-paste, multi-spot soldering are all terms used to describe a reflow process that allows through hole components to be soldered without the need for wave soldering or purchasing selective soldering systems. With the growing interest in lead-free soldering there is also a need to simplify the process stages in manufacture, particularly with many companies in Europe looking to adopt an environmentally friendly process.

The complete Pin-In-Hole Reflow (PIHR) process is to be featured at the Productronica Exhibition, one of the largest electronic assembly shows in the world and a must for engineers to get up to date with technology. We are delighted to be involved in a production line featuring PIHR assembly on Stand 205 in Hall B5. The production feature is being organised on the Harting Connector stand and features the following companies:

The Pin-In-Hole Process - Click here to get the paper

The basic PIHR process starts with stencil printing the surface of the board with solder paste. Traditionally stencil printing is conducted for surface mount terminations but with PIHR solder paste it is also printed over the through hole pads and into the holes. On the production line a tin/silver/copper alloy will be used printed through a 0.006" 150um stencil.

To see the printing process click here (To see the video clips you will need to have RealPlayer loaded on your machine. This can be downloaded here free)

The paste volume printed on the surface of the board is determined by the pitch of the connectors and the standoff features of the connector body. Good design of the connectors allows the paste volume to be maximised on the surface of the pads and onto the surface of the solder mask. Guidelines on paste, stencils and paste volumes required will be available at the exhibition with process reports and technology updates.

The printing process used will feature a sealed print head which has the benefit of increasing the penetration capability of the paste into the hole as well as well as minimising the waste associated with traditional blade printing processes.

After printing, surface mount components may be placed on the surface of the paste prior to insertion of the connectors into the pasted through holes; depending on the design the connectors may be inserted first. It has often been difficult for engineers to automate the odd form assembly process due to the need to invest in additional odd form equipment. Now with selected placement machines having the capability to insert all the popular surface mount shapes and odd form parts it opens up the opportunity for greater use of PIHR technology. The printed board design will feature three connectors, 0201 and 0402 chip components as well as BGA, Flip Chip and QFP parts.

The example shows a connector inserted in the through holes after printing of solder paste.

When assembly is complete the board passes through the reflow process to simultaneously reflow the surface mount and the through hole joints in one operation. The reflow process should be conducted on a pin transfer conveyor to avoid contact with the pasted pins. The size of the oven in terms of length and number of zones will be dependent on the throughput required. It is important to correctly profile the board assembly as the connector may be the largest component on the surface of the board in terms of mass so the through hole parts should be one of the areas selected to monitor and check the differential temperature on the surface of the board.

During production selected areas of the board will be monitored. Thermocouple leads will monitor a range of termination points on the surface of the board. This will be done to optimise the process for surface mount, through hole and lead-free assembly.

To see the PIHR process close up click here (To see the video clips you will need to have RealPlayer loaded on your machine. This can be downloaded here free)

In the case of a double sided surface mount assembly the connector side of the board would be processed second. However, it is also possible to process connectors and other through hole components on both sides of the board if required.

The following are typical examples of solder joints produced with the PIHR assembly process. The solder joint strength and long term reliability are no different than with conventional wave or manual soldering operations. The joints also meet the visual requirements for national and international standards like IPC610.

The X-ray images show through hole joints after reflow with complete fill of the barrels of the holes.

For further information on the companies participating on the production line go directly to their individual web sites

Alpha Fry Technologies www.alphametals.com
Assembleon www.assembleon.com
Harting Connectors www.harting.com
Merlin Circuit www.merlincircuit.co.uk
Nutek www.nutek-europe.com
Purex www.purexltd.co.uk
Speedline Technologies www.speedlinetechnologies.com
ECD www.ecd.com

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