We process a double-side reflow board (10 ups). Chips and IC's on the bottom side while chips, IC's plus thru-hole connectors and IC sockets on top side (bottom side first then top side reflow). In the past, we were not encountering any soldering problem with our connectors (balls at the tip of the double-header connector pins and no solder at the plated thru-hole bottom side, it looks insufficient solder on the base where fillet should form. The current oven profile (Omniflo 7, SuperMole DeLuxe) as compared to the previous ones, shows no variation. The problem problem consistently occurs on one side/row of the double-header connector which makes me think that this particular location is where root cause lies. Tried to vary the oven parameters, without going far from the current profile but the problem gets worse (more balls at the tip, insufficient solder fillet at the bottom side - connectors are inserted on the top side). Tried to simulate the problem by: 1. reversing the loading direction of boards onto the oven and the problem remains on where it occurs (one row of the connector). 2. reversed the mounting orientation of the connectors (to check whether the problem occurs on same row of the connector or remains in that particular holes of the pcb) Result: After reversing the connector, the defect followed. This makes me think that the problem lies on the one side/row of the connector material.
I viewed the connector with a microscope but I found no difference between them (color, plating, pin thickness, length of protruding pins). There was also no changes on the Plated Thru-Hole finish, diameter etc.
Tried to use a single header connector with the same finish, plating, color, thickness, length of protruding pins and oven parameters, THE PROBLEM DISAPPEARED.
What does this tell me? Anyone out there who'd be generous enough to help me? ----
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