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Non-wetting: PTH on double-side reflow

#33571

Non-wetting: PTH on double-side reflow | 6 April, 2005

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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Indy

#33573

Non-wetting: PTH on double-side reflow | 6 April, 2005

did you try using double header connector pin of a different lot?

Indy

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#33574

Non-wetting: PTH on double-side reflow | 6 April, 2005

Hi SMT Engr

With a double-header connector do you mean Double Level Right Angled Header Connector. If so there is a big difference in heat sinking capacity between the two rows, as where the pins of the top connector absorbes twice as much heat as the bottom ones. I would attach a thermo couple to one pin on both rows and look at the difference, and adjust the profile according the findings.

hope this helps, Pat

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#33576

Non-wetting: PTH on double-side reflow | 6 April, 2005

I've tried a different lot of the same double header connector (yes its double level right angled header conector) twice but nothing has improved. I've also suspected that top row of the connector has greater heat sinking capacity (which should hold true) but the problem occurs on the bottom row. If the top row has to absorb more heat than the bottom one, then top row should have the tendency to wet slower than the bottom one, hence, a soldering problem. Was the balls on the tip caused by too high temp or lower temp (higher/lower than what is required)? How do you explain that? Take note that I use the same profile for a board of almost the same size but with more thru hole parts on the top side(single header conn, DIP type IC's, radial capacitors), and there is no problem with the solder joints. One of my night-shift guy just opened the top cover of the oven and the problem is gone. Of course nobody wants an open cover all the time (LOL). :)

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#33579

Non-wetting: PTH on double-side reflow | 6 April, 2005

Soldering PTH in reflow makes the process a lot more dependent on the physical forces in soldering (capillary force vs. gravity). Reducing the topheat in your oven will help the capillary forces (opening the hood solved the problem). Heat rises so if you heat mainly from the bottom this will automatically improve cappilarity. Too much topheat will block cappillarity. Give it a try it will work.

Pat

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KEN

#33584

Non-wetting: PTH on double-side reflow | 6 April, 2005

Are you saying you have solder balls (as in solder paste balls) at the lead tips (or land tip)? This means your thermal profile is not hot enough. why the sudden cahnge? I will bet the lead frame material was copper and is now alloy 42. sounds like your profile was marginal to begin with.

Also, when you profile are you using a loaded board?

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#33586

Non-wetting: PTH on double-side reflow | 6 April, 2005

It is the solder ball that's usually encountered in a reflow process. It's just that, the paste did not wet well along the connector pins. Before reflow, the paste is actually at the tip of the connector, and stayed there and never went up to fill the PTH (no fillet).Thus forming the ball at the tip of the connector.

Well anyway, I wanna thank you guys for sharing your knowledge. I am gonna simulate further on my profile , bearing in mind your inputs. 'Will try them. If you have any further info, I'd be more than glad to see them on this thread! :)

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Bryan

#33684

Non-wetting: PTH on double-side reflow | 13 April, 2005

Can you please decrease the ramp rate of your reflow profile?In my opion,if you heat the pin too fast,the solder will drop for the gravity and the cappilary force can't draw it back.On the row with much heatsink,this issue won't happen,that's the reason. I'm not very sure about this,can you please have a try? Bryan.she@163.com

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Bryan

#33878

Non-wetting: PTH on double-side reflow | 25 April, 2005

Some weeks has passed,Can SMT eng. show us your results of this issue?so that we can learn something from it

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