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Subject:	Re: Formula for weight/surface tension to keep bottomside parts on?
From:	John Belcher <[log in to unmask]>
Reply To:	TechNet E-Mail Forum.
Date:	Tue, 21 Jan 2003 14:32:24 -0800
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MessageThanks Guy. Just what I needed.
John Belcher
  ----- Original Message ----- 
  From: Guy Ramsey 
  To: [log in to unmask] 
  Sent: Tuesday, January 21, 2003 2:17 PM
  Subject: Re: [TN] Formula for weight/surface tension to keep bottomside parts on?


  There are two methods. Joint Perimeter Length and land area. 
   
  The rule for land area is 30 g / sqin (about 47 mg / sqmm). This conservative estimate works unless the component lead is much smaller than the land.
    
  The Joint Perimeter Length rule is 188 mg per cm of JPL. This optimistic method works if the lead to land interface is about equal and wetting is good and strong. Remember is not just surface tension that holds the part on the board, wetting plays a part as well. If part of the interface is not solderable . . . plunk.
    -----Original Message-----
    From: TechNet [mailto:[log in to unmask]] On Behalf Of John Belcher
    Sent: Tuesday, January 21, 2003 3:58 PM
    To: [log in to unmask]
    Subject: [TN] Formula for weight/surface tension to keep bottomside parts on?


    Does anyone know the formula for calculating (weight versus contact area) whether a component will stay on the bottomside of a PCB?
    Thanks
    John Belcher
    Hunter Technologies
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