Hello, Zhiwei:
    It's normal that big component drop on the top reflow. If we can't change design, we need change our process. Now many SMT with both bottom and top with reflow process.
    Firstly we have bottom reflow first. Then we print solder paste on the top, pick up and place component, after this, we place the board on a fixture to go reflow together. The fixture is made by a material looks like plastic, it can prevent hot air get into bottom. If you need help on it, please send a mail to me, I will take a picture for you.
       
    Thanks!
    John Ling
    Loud China
  
----- Original Message -----
From: [log in to unmask] href="mailto:[log in to unmask]">Mike Wood
To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]
Sent: Monday, December 31, 2007 11:23 PM
Subject: Re: [TGA] Need your help to find solution that big component drop when reflow


Hi Jerry

Our assembly person at MacDermid had the following comment to your request:

There is relationship between the weight of the component and wetting force.
If the large component has more leads(terminations)  the component will survive provided the cumulative wetting forces of all leads is greater than weight of component.

What is the component, weight and number of leads(termination).

Components that usually fall off are crystals and large capacitors.

Best regards,
Mike Wood




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[TGA] Need your help to find solution that big component drop when reflow





All
 
        Do you have experience that the big component drop when reflow?
        We have layout with big components on the bottom side, when we reflow the top side, the big component would drop or find nonwetting defect, would you like to share your experience on this?
 
    Thanks and regards!
    Jerry Shen
    GE Healthcare Wuxi
    Supplier Quality Engineering