Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Lead free rework of BGA

Views: 1496

Jeff

#46742

Lead free rework of BGA | 17 January, 2007

Hi,

I am having problems reworking a lead free PBGA (23mm x 23mm, 1mm pitch). The board is relatively small (5" X 4" X 0.063"). During the removal stage, a thermocouple was placed at the solder ball level (between the board and underneath of component) to create a profile. Profile details are as follows:

Ramp Up: 20 Celsius - 140 Celsius @ 2.5 C/secdond Soak: 140C - 170C for 75 seconds Ramp Up: 170C-220C @ 2 C/second Time above 217C: 100 seconds Peak Temp: 245C Time Between: 230C- 245C = 60 seconds

After a component is removed, residual solder is cleaned off the pads on a board. Solder paste (lead free) is then transfered to the board using a mini stencil. Component is aligned using the optics of a rework station and installed. After the board cools it is tested however, have yet to see one functional . . . tried on 4 different boards. Even tried rework on functional boards . . . ended up turning a functional board into a scrap / rework one. Below are links to X-ray images of the component after rework. Can someone please review them and advise what defects are visible and any suggestions would greatly appreciated.

1. http://server4.pictiger.com/img/847618/other/all-balls.php

2. http://server4.pictiger.com/img/847619/other/close-up-view.php

3.http://server4.pictiger.com/img/847620/other/tilt-view.php

Thanks

reply »

#46754

Lead free rework of BGA | 17 January, 2007

When placing the part to be reflow try applying heat to the board from the secondary side until the primary side has a temperature of about 130 degrees celcius. Following this procedure it should minimize the heat exposure of the part being soldered. I checked the X-ray pictures, some of the balls do not seem to be round in shape, there are some voids in there as well, but that it should be part of the design. It could be that the flux from the solder paste was burnt earlier before the board reach the solder melting point. Hope this helps.

reply »


RDR

#46758

Lead free rework of BGA | 17 January, 2007

appears to be incomplete reflow on a couple of balls or they were moved during a cooldown. it also seems as though there is a deviation in ball size due to inconsistant paste application possibly.

I would stop applying paste and just reflow that part as is with your profile, use a real good no-clean paste flux for the reflow.

Russ

reply »

Jeff

#46782

Lead free rework of BGA | 18 January, 2007

So you are suggesting to begin heating using a preheater only . . . then when the thermocouple under my PBGA reads around 130C, turn on a top side heater?

Thanks

reply »

Jeff

#46784

Lead free rework of BGA | 18 January, 2007

Thanks. I will turn off the machine activated cooling and have the part cool down at room temp (no compressed air cooling). Can you recommend a good paste / tacky flux?

reply »


RDR

#46801

Lead free rework of BGA | 18 January, 2007

won;t recommend a paste since I propose that you do not use but here is a flux I have had great success with

Indium tacflux 20B IPN 84283

No clean flux, Use this alone without paste and your BGAs will work!!

What was your package temp during this reflow process? I know you had balls at 245 but what about the case itself?

Russ

reply »

Jeff

#46811

Lead free rework of BGA | 18 January, 2007

Thanks Russ. I meant paste flux or as some refer to it tacky flux (I think it's the same thing). I will try to get some of that Indium flux. Hopefully they will sell us 1 or 2 syringes.

>>What was your package temp during this reflow process? I >>know you had balls at 245 but what about the case itself?

I did not measure the temperature of a package. My thermocouples are 36AWG - around 0.01" diameter, so about the only way I imagine measuring the package temperature is to place one on top surface and tape it down hoping that the tip is in contact with a component. The idea is to check that the package does not exceed 250C?

reply »


RDR

#46833

Lead free rework of BGA | 19 January, 2007

yeah Jeff, i would make sure that you are not overheating part trying to get the balls to temp.

Indium will sell you a couple of these cartridges for sure.

Good Luck

Russ

reply »

Reflow Oven