We agree with Wolfgang. Adding points along his line of reasoning: * Also consider placed component prescience. Sometimes, a mis-pick results in paste on the nozzle, which leads to the next component being stuck on the nozzle and not placed, which leads to additional mis-picks. * Continuing, people have related experiences of moving components from the placed position during reflow with hyper-active blowers, but we have never seen it done. * Finally, biggest clue to the cause of your missing components is the missing components. It you find a neat little [hopefully little] pile of parts, the cause of your angst is not far up-stream.
Now responding more directly to your question, we use a tack test [probably not unlike the test Bill suggested] to compare the characteristics of solder pastes as an element of a paste qualification, but not as the production process control that you suggest. In this qualification, we perform a �
5.2 Post-Placement Tack Test
5.2.1 Using the stencil described in paragraph 3 above. [NOTE: We use our stencil for a variety of paste tests. For this test, printing an array of approximately 100 parts using production standard pad layout is sufficient.] Print paste on a bare board or laminate.
5.2.2 Place 1206 (or 0805) discrete components in the paste.
5.2.3 Wait one hour.
5.2.4 Gently, invert and support the board above a table.
5.2.5 At one hour intervals, record the number of components that have fallen from the board.
Tell us more about the details and distribution of the situation that makes you question the adhesion properties of your solder paste.
reply »