Double Sided Reflow - Components on Bottom Side

Does anyone have a list of component types that can be put on the bottomside of a doublesided reflow board that will not fall off during the second pass (Or on the otherhand, a list of components that will fall off)? This would be a list of parts that can be held in place by surface tension alone (No glue, special reflow profiles or multiple solder types allowed). Obviously small chip type components are candidates but what about larger components (BGA's, QFP's PLCC's, etc.). If you do not have a list, how about some design guidelines. I have heard that if the ratio of the weight of the part in grams to the total pad contact area of the part in sqcm is less than 5, the part will not fall off. This seems like it would tke allot of unnecessary time to compute for each part. Suggestion to part vendors: In the part datasheet, list whether or not the part can be subjected to a second reflow in the inverted position without falling off. Any help would be greatly appreciated.

reply »