Determine Hole Size for Plastic Peg Alignment Pins

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Dear FPX people,

Are you willing to explain to me the IPC recommended way to determine the correct NPTH hole size for plastic peg alignment pins?  
I will be using the Molex 87782-3003. This is an MiniDIMM socket with two plastic alignment pins, a round one with a diameter of 1.4 mm and an rectangle measuring 0.8x1.3 mm. It is especially important to me because I intend to place two of these sockets inline and we will be developing plugin cards that need to connect to both sockets.  
Do you know if a large difference of the glass transition temperature or Tg value between the MiniDIMM socket and the PCB matter for reliable reflow soldering? A person of an assembly facility told me about Tg values. What is your opinion on that?

Thank you very much for your attention and time!

Best regards,
Maarten Verhage

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Maarten Verhage Members Profile Send Private Message Find Members Posts Add to Buddy List Active User Joined: 27 Jul 2012 Location: Netherlands Status: Offline Points: 27	Post Options Post Reply Quote Maarten Verhage Report Post Thanks(0) Quote Reply Topic: Determine Hole Size for Plastic Peg Alignment Pins Posted: 03 Dec 2012 at 3:01am
	Dear FPX people, Are you willing to explain to me the IPC recommended way to determine the correct NPTH hole size for plastic peg alignment pins? I will be using the Molex 87782-3003. This is an MiniDIMM socket with two plastic alignment pins, a round one with a diameter of 1.4 mm and an rectangle measuring 0.8x1.3 mm. It is especially important to me because I intend to place two of these sockets inline and we will be developing plugin cards that need to connect to both sockets. Do you know if a large difference of the glass transition temperature or Tg value between the MiniDIMM socket and the PCB matter for reliable reflow soldering? A person of an assembly facility told me about Tg values. What is your opinion on that? Thank you very much for your attention and time! Best regards, Maarten Verhage



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5718	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 29 Dec 2012 at 2:51pm
	The Tg (Glass Transition Temperature) relates to the PCB expansion in the "Y" axis or board thickness. Or the temperature at which material or areas of material changes from being in a hard condition to being a viscous or rubbery condition. The CTE (Coefficient Thermal Expansion) relates to the PCB expansion in the "X" axis or board length and width. Or the linear dimensional change of material per unit change in temperature. You can avoid both conditions by using high temperature material. Plastic alignment pins on connectors are used to register the package to help the SMT component leads line up with the pads. Most connector manufacturer's provide the recommended hole size for the alignment pegs. I mean I've never built a connector library part where the mfr. did not provide the recommended hole size. But if you had to calculate a hole, it would be non-plated with a +/- 2 mil (0.05 mm) tolerance and 2 mil larger than the maximum peg diameter. We just added a new padstack calculator to the PCB Footprint Expert. In the main toolbar select the "Utilities > " TH Padstack Calculator" dropdown.