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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


BGA REFLOW

Views: 7737

#63444

BGA REFLOW | 7 January, 2011

Hi Smarts We are having difficulty in reflowing BGA wiht ROHS process on double sided board. We have tried profiling un populated board and profile is meeting upper spec of solder paste. but our customer is saying they have to heat up BGA and board starts working fine. Our task is to establish why solder is not melting even with upper spec of reflow (250Degree peak and 55sec reflow time Dwell time). Please reply suggestion we have to try considering we dont have xray machine Ripal

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#63446

BGA REFLOW | 7 January, 2011

What failure analysis have you done to know that the solder isn't melting?

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#63447

BGA REFLOW | 7 January, 2011

Consider measuring the temperature of the BGA solder balls during reflow. This will give you a more accurate impression of the actual soldering temperature than you are getting now.

The 1/6/2011 SMT Express Newsletter‏ contained an interesting article on BGA soldering temperature measurement "Evaluating The Accuracy Of a Nondestructive Thermocouple Attach Method For Area-Array Package Profiling." http://www.smtnet.com/express/

We receive no benefit from the companies that sponsored the article.

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#63453

BGA REFLOW | 7 January, 2011

We havn't done any failure analysis on this BGA. We have this information from customer. currently we dont have anything to check solderability for BGA. Only thing we rly is Profile on solder sample un populated board. Also we are building only 100 units and there is no scrap board available.

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#63454

BGA REFLOW | 7 January, 2011

we are building only 100 units and there is no scrap board available. How can we make sure without distrubing good board that BGA is flowed properly?

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#63455

BGA REFLOW | 7 January, 2011

Tell your customer that you need five extra assemblies so that you can do a good job of designing process to ensure that they don't receive poo boards.

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#63472

BGA REFLOW | 10 January, 2011

Hi Ripal it seems that you have problem with compatibility of alloy and quality of solder balls. First check solder alloy form BGA balls what is it?(SAC105,SAC305, etc.) what type of solder paste you use?? third thing is what type of finishing you have surface on on pcb (finishing) when you check , i hope the answer will be easy sometimes person who make project pcb with comonents don't thinks about solderability.

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Say

#63488

BGA REFLOW | 11 January, 2011

Use the Kester solder paste EM828 SAC305. Guarantee good reflow. Peak@250 Reflow@80s Soak@75s.

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#63492

BGA REFLOW | 12 January, 2011

Do you think it is because of too much solder. we have 5thou stencil and no reduction in aperture. Please reply

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#63505

BGA REFLOW | 12 January, 2011

HI Ok solder past seems to be ok, but what type do you have finihing of PCB(ENIG, immersion silver, SN100??), second what type of solder alloy do you have on BGA, its important, I don't think that you have problem with stencil. answer on my question and we will be thinking what do next

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#63641

BGA REFLOW | 27 January, 2011

Hi, We had a similar issue to this. When we examined the boards at x-ray there were no apparent defects, We sent the boards for Dye and pry testing and we found that there were crack or gaps between the paste on the PCB and the BGA ball. basically the paste reflowed, the ball reflowed but they did not coalesce due to a build up of oxidation. This can occur if 1) the part warps during reflow creating a gap between the ball and paste 2) the flux is burnt off too early so there is no oxidation barrier during reflow. What we did initally to overcome this was to remove the soak zone and reduce the peak temperature to 240 on the larer BGA's. This allowed the flux to be active for longer and prevented the oxidation. We are now looking at alternative paste, indium 8.9 is marketed on its ability to eliminate head -in -pillow defects, So far its looking good.

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CL

#63672

BGA REFLOW | 1 February, 2011

good Morning,

it looks from the peak temperature that this is a RoHS application? If so, is the BGA that you are having issues with leaded? If so, you might be experiencing "ball drop" where the ball becomes disconnected from the component substrate. Reheating back to liquidous can re-establish electrical contact. Usually, flux is required to accomplish this.

I agree with the statement on the Kester EM828 solder paste. It reflows great. I have had cleaning issues with that material in DI water.

good luck

Chris

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