SMART Group

SMT is part of mainstream electronic assembly with virtually all market sectors benefiting from its use. One problem that has always proved an issue to design and process engineers is the use of existing through hole components where no direct equivalent SMT parts are available. Some people said that through hole parts would disappear completely in the industry, how wrong they were!!

One method of soldering all surface mount and through hole components in a single operation is Pin-In-Hole-Reflow (PIHR) or Intrusive Reflow Soldering which simplifies the manufacturing process and is totally compatible with lead-free assembly. It also requires little or no investment in capital equipment and has equal joint reliability to wave, selective and hand soldering. This is one of the workshops regularly run by SMART with the first event run in the mid 90's when the process was first used in manufacture.

Presentations were given by Doug Black and Alan Hobby of DEK and Bob Willis, Technical Director of the SMART Group. Each delegate received a copy of the presentations, SMART Group Pin In Hole Design and Reflow Guide, Ten Point PIHR Checklist and a set of Colour PIHR Inspection Posters.

Each presenter demonstrated that the process is simple and with a little thought can be helpful to eliminate the problems faced with lead-free wave soldering of through hole parts. Willis and Hobby have been doing pin in paste for years and it showed!!!

SMART Group members can get a copy of the presentations from the members area of the web site.

The workshop covered the following key points:

PCB Design and Component Requirements
PIHR Advantages and Disadvantages
Paste Application by Stencil Printing, Double Stencil Print, Dispensing
Stencil Aperture Calculations
Solder Pallet Support
Component Insertion
Reflow Soldering Profiles
Lead-Free Implications
IPC Inspection Requirements
Practical Applications
Process Defects

The hands on session in the afternoon put the theory into practice and allowed delegates to stencil print lead-free paste with standard metal blades, sealed head printers and a see a mixture of different PCB surface finishes being processed. Connectors from Harting were used to demonstrate the PIHR process.

During the final session delegates were offered the opportunity to visit the stencil manufacturing facility and the printer assembly lines. All agreed it was a great day and worth the long drive to sunny Weymouth.

Pin In Hole/Intrusive Reflow Check List

1. Are your through hole components compatible with reflow soldering temperatures? Do they meet the minimum requirement of the IPC/IEC component compatibility standards of 230oC for 30 seconds ?

2. Can you obtain the through hole components in packaging suitable for automatic assembly? Manual assembly is possible but automation will improve consistency.

3. Have you calculated your through hole and lead to hole ratio for automatic and manual insertion ? You may have to do this if you normally group holes to reduce the number of drill sizes in printed board manufacture. Lead size plus 0.010" is normal.

4. What standoff height do you have on the components and where are the component standoff feet located will they contact your paste deposit? A minimum standoff height should be 0.010"

5. Have you tested your solder resist with your solder paste during reflow, does it cause solder balling? It is often necessary to print paste on to the resist to obtain the correct volume of solder to fill the hole after reflow.

6. Have you calculated the stencil thickness required to fill your plated through holes with solder after reflow? The following calculation will provide a basic initial guide:

Volume of Paste = (Volume of PTH - Volume of pin) x 2

7. Have you told your stencil manufacturer that the through hole apertures are required on your new stencil? Normally we tell the stencil supplier to take them out, don't we? Also have you shown your supplier a connector?

8. Have you discussed changes to your soldering standards for Pin In Hole Reflow Assembly with your quality department and your customer? You can achieve 100% fill but positive fillets are more difficult. The joints will also look different !

9. Have you specified your component lead lengths and can you control them? Lead length control is crucial and should ideally give a protrusion of 1-1.5mm below the board.

10. Do you know how strong solder wave and hand soldered joints are? They are no different than through hole reflowed joints but remember, someone will ask you !

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