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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Cracking Capacitors

Rich Weaver

#14430

Cracking Capacitors | 3 September, 1998

I am in need of possible causes and solutions to capacitors that are failing in the field. Are there issues in our process that need to be checked? Some people said the problems are due to improper storage. Others say it is thermal stress in our reflow (we don't believe this is the case). Could you please offer suggestions as what to look for. Best regards.

reply »

Ben Salisbury

#14439

Re: Cracking Capacitors | 3 September, 1998

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. Rich- What tests have you run to rule out the possibility of it being your reflow profile. So far this has been the only cause that I've seen in our process. In the pre-heat section of your profile, is where the case of thermal shock normally occurs...Caused by a ramp-up that is one-to steep and second-to hot. Another possible reason, I havn't personally experienced this one yet...Knock on wood...but moisture trapped in the component will expand and cause a popcorn like effect during reflow. but that problem would would show up at ICT. I guess this would leave another question for the more knowledgable people on the channel, would entraped moisture cause degradation of the component over time. Or in the case of capasitors, is it possible to have a partial popcorn, and not brake the casing...but weaken it, and thusly due to thermal and environmental stress in the field cause it to degrade and fail? Just a thought -Ben

reply »

Dave F

#14438

Re: Cracking Capacitors | 3 September, 1998

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. Rich: Please describe the location and orientation of the cracks on your capacitors. Are the cracks all similar? Dave F

reply »

Mike Cox

#14437

Re: Cracking Capacitors | 3 September, 1998

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. Hi Rich Here is a list of causes I have run across 1) Reflow profile 2) Caused by depanneling process 3) ICT test fixture 4) Handling (picking up a board by the edge) 5) Customer instilation/handling Good luck Mike C

reply »

Earl Moon

#14434

Re: Cracking Capacitors | 3 September, 1998

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. In addition to the other information provided, I have experienced plenty of cracking because of three things. 1) Unacceptable design rules as SMT pads or neckdown features causing cracks because of thermal stress after assembly (during operation) 2) As the above with cracking after excessive mechanical stress or shock 3) Cracking during or after repair or modification operations wherein hand soldering is improperly performed Much luck Earl Moon

reply »

Matthew Park

#14433

Re: Cracking Capacitors | 3 September, 1998

Rich, From my experience, few causes of capacitor cracking are: - mechanical stress caused by pick'n place nozzles and chucks. Try to isolate and find cracked caps before boards go thru reflow or wavsoldering. - thermal stress by reflow profile and wavesoldering processes. A sudden thermal shock when a board hit solder in wavesoldering can induce the stress. By reducing the solderpot temp and by increasing preheat temp or slowing the conveyor belt speed can reduce cap cracking. Check your temp reflow profile ramps up and absorb heat slowly. - Certain batch or maker of capacitors can not absorb slight manufacturing stresses. Change to a different cap mfg or try cap's from different batch (date code). This is the simplest way to solve cracking capacitors

Regards Matthew Park NII - Norsat International Inc. | I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards.

reply »

Pete Sorenson

#14432

Re: Cracking Capacitors | 3 September, 1998

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. Rich, since this is a SMT forum, responses to date have assumed that the capacitors which are cracking are SMT chips. In the event that these are leaded capacitors, in particular capacitors with epoxy coatings, moisture can cause "popcorn" effects as described in one of the responses. This is a problem which I have experienced, and is solved by drying the components in a vacuum oven prior to use. Storage for extended periods of time in high humidity seems to be a contributing factor. Failures, either shorts or open, may take time to develop, which allows assemblies to pass tests but fail in the field.

reply »

Mike Demos

#14431

Re: Cracking Capacitors | 8 September, 1998

Rich: In my experience, I have seen three cases of SMT Capacitors cracking: 1. Due to thermal shock when entering the wave solder. Note that these were 1210 package sizes on the wave solder side of the boards. We were able to trace this back to the manufacturer of the parts. They had a process problem where the final layer of ceramic material was too thin. We have since changed to a 1206 package size on nearly all of the boards. This size is more "forgiving" of the thermal shock when entering the wave. 2. Due to support pins in the SMT equipment. Note that these were on two-sided boards and the cracked components were on the second side placed. If the operator has a support pin positioned incorrectly, it can crack components. These are easier to diagnose because the crack is more of a "smash" and is in the same place on every board. 3. Due to vacuum nozzle damaging the components. I have seen this with older equipment but have not seen it with the newer equipment. Most chip-shooters have spring-loaded nozzles. I also have two article that I would be glad to either fax or mail to you: 1. "Assembly Induced Defects" 2. "Surface Mount Soldering Techniques and Thermal Shock in Multilayer Ceramic Capacitors" Both of these are by John Maxwell when he was with AVX and both touch on potential cracking problems in capacitors. Let me know if you like these. Thanks, Mike Demos mdemos@oconee.rms.slb.com

| I am in need of possible causes and solutions to capacitors that are failing in the field. | Are there issues in our process that need to be | checked? | Some people said the problems are due to improper | storage. Others say it is thermal stress in our | reflow (we don't believe this is the case). | Could you please offer suggestions as what to look | for. | Best regards. Rich: In my experience, I have seen three cases of SMT capacitors crackin

reply »

John Godfrey

#14435

Re: Cracking Capacitors | 9 September, 1998

| | I am in need of possible causes and solutions to capacitors that are failing in the field. | | Are there issues in our process that need to be | | checked? | | Some people said the problems are due to improper | | storage. Others say it is thermal stress in our | | reflow (we don't believe this is the case). | | Could you please offer suggestions as what to look | | for. | | Best regards. | In addition to the other information provided, I have experienced plenty of cracking because of three things. | 1) Unacceptable design rules as SMT pads or neckdown features causing cracks because of thermal stress after assembly (during operation) | 2) As the above with cracking after excessive mechanical stress or shock | 3) Cracking during or after repair or modification operations wherein hand soldering is improperly performed | Much luck | Earl Moon I never would have thought about pad size for this problem as you mention in item #1. What issues have you seen with pads size and neckdowns ?

reply »

Earl Moon

#14436

Re: Cracking Capacitors | 9 September, 1998

| | | I am in need of possible causes and solutions to capacitors that are failing in the field. | | | Are there issues in our process that need to be | | | checked? | | | Some people said the problems are due to improper | | | storage. Others say it is thermal stress in our | | | reflow (we don't believe this is the case). | | | Could you please offer suggestions as what to look | | | for. | | | Best regards. | | In addition to the other information provided, I have experienced plenty of cracking because of three things. | | 1) Unacceptable design rules as SMT pads or neckdown features causing cracks because of thermal stress after assembly (during operation) | | 2) As the above with cracking after excessive mechanical stress or shock | | 3) Cracking during or after repair or modification operations wherein hand soldering is improperly performed | | Much luck | | Earl Moon

| I never would have thought about pad size for this problem as you mention in item #1. What issues have you seen with pads size and neckdowns ? I thought no one would ask. The problems encountered mostly have been with R/F designs wherein engineers establish rules requiring device placement on large traces (to .250" wide), with no neckdowns, to ensure required electrical performance. In these cases, the copper circuitry, having a TCE of 17-19 ppm (compared with 5-7 ppm for ceramic devices), moves under thermally induced conditions during operation. Also, larger pad sizes can do the same thing with smaller or thinner device types. Additionally, when performing touch up or repair on designs having larger than "normal" neckdowns, the solder obviously drains off (as it does during reflow) often making the hand solder operator keep the iron on the solder termination areas too long (in excess of 3 or 4 seconds). They do this hoping to overcome the drain off but induce component cracking. In these cases, the situation is not much different than using LCCC's though solder joint failure is more prevalent than device damage. We all are aware of the problems so well stated by all others on this question. The thermal excursion and TCE mismatch problems are less known except to military/aerospace/RF types. Earl Moon

reply »

PCB Soldering Tools

SMT in-printer dispensing